Why does the Torah give so much detail in the War on Midyan?

Question

Moshe Rabbeinu and Israel fought a number of wars. Maybe starting with Egypt at the Yam Suf, but certainly against Amalek, Melech Arad, Sichon, and Og. Only by Midyan, apparently the last war chronologically, do we hear: The size and makeup of the army sent against them. A fuss about which prisoners were spared. The quantity and division of the spoils, in very great detail. There are further details on a tax imposed. Also there was a special gift by the leaders of the army. And the basis for our laws of hagalas keilim and t'vilas keilim are stated there. Did some or all of these apply in earlier wars? We know spoils were taken from Sichon and Og at least, see Parshas Devarim 2:35, 3:7; presumably some of those were pots as well. Why is this war described in so much detail?
Update: Given some of the comments, I think I should take hagalas keilim off the list. There are a number of (local) reasons given for that one, starting with the Ramban (Bamidbar 31:23).

Answer 1

Here is a link that discusses a novel approach to the Midyan war and it's similarities to the Chet HaEgal that can possibly answer these questions.

https://www.etzion.org.il/en/tanakh/torah/sefer-bamidbar/parashat-matot/matot-latter-generation-and-war-midyan

Answer 2

A partial answer; others may edit.

1. All the good had already been "harvested" from Midian, namely Tziporah, and no more good was to come from Midian, unlike Moab where David was still to come.

2. The most pernicious attack of the Baal Peor cult and heresy was entirely due to Midian.

Zohar III:188a ff., P. Balak
[all caps = commentary of translator Michael Berg; bold emphases added]

60. One day, the friends were sitting and contending with each other, MEANING THEY WERE HAVING A DISCUSSION AMONG THEMSELVES. Rabbi Elazar, Rabbi Aba, Rabbi Chiya, Rabbi Yosi and the rest of the friends were present. They said that it is written: "Do not harass Moab, nor contend with them in battle..." (Devarim 2:9). That was for the sake of Ruth and Naamah, who were destined to come from their midst. AND IF SO, Tziporah, the wife of Moses who came from Midian, and Jethro and his offspring, who came out of Midian, who were all truly just, most certainly SHOULD HAVE PROTECTED MIDIAN. Furthermore, Moses grew up in Midian and still, the Holy One, blessed be He, told him, "Execute the vengeance of the children of Yisrael on the Midianites" (Bemidbar 31:2), YET MOSES' MERIT DID NOT PROTECT THEM. Therefore, there is an inappropriate bias in this matter, since Midian appeared worthier to be saved than Moab.

61. Rabbi Shimon said, There is no comparison to the one who is going to gather the figs to the one who already gathered them, SINCE RUTH AND NAAMAH HAD NOT YET EMERGED FROM AMON AND MOAB, WHICH IS NOT THE CASE WITH TZIPORAH, WHO HAD ALREADY EMERGED FROM MIDIAN. Rabbi Elazar said to him, Although they already gathered THE FIGS, it is still a merit AND THEY SHOULD HAVE BEEN SAVED IN THEIR MERIT. He said to him, Like whoever has not collected the figs yet constantly guards that fig tree, so that it should not get any harm for the sake of the figs that are still to grow in the future. He abandons the tree and does not watch it after collecting the figs.

62. So with Moab, that was to produce in the future these figs, RUTH, AND HER OFFSPRING, the Holy One, blessed be He, guarded them, as it says, "Do not harass Moab." Midian had already produced the figs and they were collected, as it is written: "Vex the Midianites" (Bemidbar 25:17), since from here on, this fig tree will no longer produce fruit. Therefore, it deserves to be burned by fire. He opened the discussion saying, "And Moab said to the elders of Midian..." (Bemidbar 22:4). Moabites are the ones who started TO DISTRESS YISRAEL. For the sake of the figs, RUTH AND HER OFFSPRING, that Moab is destined to produce in the future, they were saved from punishment.

...

93. He [the toddler, "Yanuka," child of R' Hamnuna Saba] opened by saying, "And Moab said to the elders of Midian" (Bemidbar 22:4). HE ASKS: It does not say, 'The elders of Moab said to the elders of Midian', but "Moab said." That means that the young OF MOAB took counsel of the elders OF MIDIAN, and the older ones followed after THE WISHES OF THE YOUNGER ONES and gave them advice. What was the advice with which they counseled them? They took for themselves bad advice. The ELDERS OF MIDIAN said to Moab, We have grown a bad crop among us. And who is it? It is their master, Moses. There was among us a priest who took care of him and supported him in his house and gave him his daughter for a wife. Furthermore, he gave him money and sent him to Egypt to destroy the whole country. And he, THE PRIEST, and his entire household got carried away after him. If we could root out from the world that master of theirs, all his people would be uprooted from the world. The entire disastrous advice in the matters of Pe'or stemmed from Midian.

94. Come and see that everything stemmed from Midian; the thrust of their counsel was about Moses, and with the advice of Midian they hired Bilaam. When they realized that Bilaam was incapable, they followed another bad idea, and they freely loosened their women and daughters even more than Moab. About the women of Midian, it is written: "Behold, these caused the children of Yisrael..." (Bemidbar 31:16). Everything stemmed from Midian. They took counsel with their chief that he should loosen his daughter, since they were plotting to ensnare Moses in their net. They adorned her with how many spells, so she should successfully catch the head OF YISRAEL. And the Holy One, blessed be He, "turns wise men back" (Yeshayah 44:25).

...

96. Everything originated in Midian in several ways. Therefore, Midian was punished and the Holy One, blessed be He, said to Moses, "Execute the vengeance of the children of Yisrael on the Midianites" (Bemidbar 31:2). For you, it is appropriate and becoming. As for Moab, I leave them alone until the two jewels will come out from among them. Here's David son of Yishai who will take revenge on Moab, and will rinse the loaded pot of filth from Pe'or. This is what it says, "Moab is my washpot" (Tehilim 60:10) assuredly. As long as these two jewels did not come out of there, they were not punished. As soon as they came out, David came and washed clean the pot from their filth, and all received their punishment, Midian during the time of Moses and Moab during the time of David.

97. Come and see that, in spite of all this, the wicked of Midian did not rest from all their evil. Generations later, when they saw that Joshua had died, together with all the elders who were worthy to have miracles caused through them, they figured that the time was now opportune. What did they do? They approached Amalek and told them, It is worth it for you to remember what the children of Yisrael and their master Moses and his disciple Joshua have brought upon you that will destroy you from the world. Now is the opportune time, for they have no one to shield them. We will go and accompany you, as is written: "Midian and Amalek and the children of the east..." (Shoftim 6:33). "And because of Midian the children of Yisrael made for themselves the tunnels..." (Ibid. 2). There was no one in the world who wished to harm the children of YISRAEL like Midian. You might say Amalek; because of jealousy of the covenant, they approached the covenant TO HARM IT. Therefore, the Holy One, blessed be He, took everlasting vengeance, which was not to be forgotten. They agreed that it was certainly so and there was no doubt in the world.