The Prophet Malachi is the commonly accepted latest prophet. The latest book of the Tanach (Daniel) is about 250 years later. Is there a reason why prophecy is understood to have ended or why later prophets could not be expected? I am not asking for speculations but rather sources from Tanach or Talmud.
Though I disagree with your premise about the dating and status of Daniel, nevertheless, that's not your question, so here are the sources I can think of to answer your question.
Our sages explain that there was no prophecy because the Shechinah or Divine Presence was no longer around beginning from the deaths of the last three prophets, Chagai, Zecharyah and Malachi. As is written in Sanhedrin 11a (emphasis mine):
"Since Shmuel HaKatan and his great piety were mentioned, the Gemara now relates several incidents that shed additional light on his personality. The Sages taught: After the last of the prophets, Haggai, Zechariah, and Malachi, died, the Divine Spirit of prophetic revelation departed from the Jewish people. But nevertheless, they were still utilizing a Divine Voice, which they heard as a kind of echo of prophecy. One time, a group of Sages were reclining in the loft of the house of Gurya in Jericho, and a Divine Voice was bestowed upon them from Heaven, saying: There is one here who is fit for the Divine Presence to rest upon him as it rested upon Moses our teacher, but his generation is not deserving of this distinction. The Sages set their eyes upon Hillel the Elder, trusting that he was the one indicated by the Divine Voice. And when he died, the Sages said about him: Alas, the pious man, alas, the humble man, a disciple of Ezra. The baraita continues: Another time, a group of Sages were reclining in the loft in Yavne, and a Divine Voice was bestowed upon them from Heaven, saying: There is one here who is fit for the Divine Presence to rest upon him in prophecy, but his generation is not deserving of this distinction. The Sages set their eyes upon Shmuel HaKatan. And when he died, the Sages said about him: Alas, the pious man, alas, the humble man, a disciple of Hillel."
The same story also appears in the Tosefta Sota 13:5, Bavli Sota 48b, Yerushalmi Sota 45b and Shir Hashirim Rabbah 8:9:3. Similarly, it says in a few places - Avot D'Rabbi Natan A 14:1, Avot D'Rabbi Natan B 28:1, Sukkah 28a, Bava Batra 134a:
"Hillel the Elder had eighty students. Thirty of them were sufficiently worthy that the Divine Presence should rest upon them as it did upon Moses our teacher..."
And Rabbi Abba said of Rav Huna when he passed away (Moed Katan 25a):
"Rabbi Abba opened his eulogy for him: Our Rabbi was worthy that the Divine Presence should rest upon him..."
Last summer I heard a fascinating class by Rabbi Yoel Bin-Nun. The class was about prophecies that predicted the leaving of the Shechinah from the Temple and hence from the Land of Israel. Based on what the sages tell us, we may infer that these prophecies also predicted the disappearance of prophecy, too. There are thus three such prophecies in Tanach:
"In the year that King Uzziah died, I beheld my Lord seated on a high and lofty throne; and the skirts of His robe filled the Temple. Seraphs stood in attendance on Him. Each of them had six wings: with two he covered his face, with two he covered his legs, and with two he would fly. And one would call to the other, “Holy, holy, holy! The LORD of Hosts! His presence fills all the earth!” The doorposts would shake at the sound of the one who called, and the House kept filling with smoke. I cried, “Woe is me; I am lost! For I am a man of unclean lips And I live among a people Of unclean lips; Yet my own eyes have beheld The King LORD of Hosts.” Then one of the seraphs flew over to me with a live coal, which he had taken from the altar with a pair of tongs. He touched it to my lips and declared, “Now that this has touched your lips, Your guilt shall depart And your sin be purged away.” Then I heard the voice of my Lord saying, “Whom shall I send? Who will go for us?” And I said, “Here am I; send me.” And He said, “Go, say to that people: ‘Hear, indeed, but do not understand; See, indeed, but do not grasp.’ Dull that people’s mind, Stop its ears, And seal its eyes— Lest, seeing with its eyes And hearing with its ears, It also grasp with its mind, And repent and save itself.” I asked, “How long, my Lord?” And He replied: “Till towns lie waste without inhabitants And houses without people, And the ground lies waste and desolate— For the LORD will banish the population— And deserted sites are many In the midst of the land. “But while a tenth part yet remains in it, it shall repent. It shall be ravaged like the terebinth and the oak, of which stumps are left even when they are felled: its stump shall be a holy seed.”"
This is of course a very famous prophecy, one of the main reasons being that it's part of our daily prayers. However, in context, its meaning is different than the way it's used in prayer. In prayer it's used to sanctify Hashem. In Tanachic context, however, it's describing one of the greatest catastrophes in Jewish history, which is Hashem's presence leaving the Temple and Israel. For this reason, rather than simply being awestruck at the sight, Isaiah cries out in mourning: "Woe is me!". Rabbi Bin-Nun explained that though the term "ושוליו מלאים את ההיכל" in modern Hebrew is understood as referring to the corners of Hashem or His clothing filling the Temple, in ancient Hebrew it actually refers to His base, i.e., Isaiah was watching Hashem launch out of the Temple like a rocket (metaphor used by the rabbi).
"I saw my LORD standing by the altar, and He said: Strike the capitals so that the thresholds quake, and make an end of the first of them all. And I will slay the last of them with the sword; not one of them shall escape, and not one of them shall survive."
The reason Amos saw Hashem stand by the altar and not sitting in the Holy of Holies was because, just like Isaiah, he was seeing Him exiting the Holy of Holies, and just before leaving the Temple, He stopped, turned to Amos, and told him of the coming days.
- Ezekiel Ch. 8-11 (it's long, so I'll bring only select verses):
"In the sixth year, on the fifth day of the sixth month, I was sitting at home, and the elders of Judah were sitting before me, and there the hand of the Lord GOD fell upon me. As I looked, there was a figure that had the appearance of fire: from what appeared as his loins down, [he was] fire; and from his loins up, his appearance was resplendent and had the color of amber...And the Presence of the God of Israel appeared there, like the vision that I had seen in the valley...Now the Presence of the God of Israel had moved from the cherub on which it had rested to the platform of the House...Now the cherubs were standing on the south side of the House when the man entered, and the cloud filled the inner court. But when the Presence of the LORD moved from the cherubs to the platform of the House, the House was filled with the cloud, and the court was filled with the radiance of the Presence of the LORD...And when they moved, each could move in the direction of any of its four quarters; they did not veer as they moved. The [cherubs] moved in the direction in which one of the heads faced, without turning as they moved...The cherubs ascended...Whenever the cherubs went, the wheels went beside them; and when the cherubs lifted their wings to ascend from the earth, the wheels did not roll away from their side...Then the Presence of the LORD left the platform of the House and stopped above the cherubs. And I saw the cherubs lift their wings and rise from the earth, with the wheels beside them as they departed; and they stopped at the entrance of the eastern gate of the House of the LORD, with the Presence of the God of Israel above them...The Presence of the LORD ascended from the midst of the city and stood on the hill east of the city..."
Ezekiel tells us of the most detailed version of the same sight seen by Isaiah and Amos1, that of Hashem's Presence leaving Israel; Ezekiel describes a gradual ascent: First Hashem leaves the inner court, then He leaves the Temple, then He leaves Jerusalem.
However, this does not mean that future prophets cannot be expected. Prophecy hinges upon the return of the Shechinah; when that happens, we can expect the return of prophecy, b"h.
1 Someone told me once that the more detailed a highly mystical prophecy is, the lower the prophetic level the prophecy was given on was (because the more spiritual something is, the harder it is to put into words). On the other hand, I read somewhere or heard somewhere that as Ezekiel was one of the last two prophets of the First Temple period (along with Jeremiah), he experienced the dying spasms of prophecy, which were very powerful, and for this merited to have these kinds of prophecies (it's also noteworthy about Ezekiel that many of his prophecies begin with the special term "son of man". As for Jeremiah, Jeremiah's prophecies echoed just about all of the prophets who came before him. He paraphrases many of them).
During the time of the Second Temple, the Sages of the Great Assembly saw that the people's ability to resist the temptation for idol worship was weakening, and realized that if the pattern continued, there would come a point when it would be all but impossible to resist. In order to avoid this situation, they prayed to G-d that he should remove the temptation for idol worship from the world, and G-d agreed to do so. Sanhedrin 64a
The Gr"a in his commentary on Seder Olam Raba says that as a "side effect" of removing the inclination towards idol worship, G-d also removed the spirit of prophecy from the world.
I have learned (thought I don't have a source offhand) that this is because the temptation towards evil and towards good must be relatively evenly balanced, otherwise humans don't really have free choice and they can't get any credit for their decisions. If G-d's word, in the form of prophecy, was readily available, yet the temptation for evil was reduced, of course nobody would sin, and therefore people wouldn't be able to get reward for their positive deeds.
See also this question from Mi Yodeya