I once heard Rav Herschel Schachter discuss this question. He gave an analogy, that if one were to bring out Euclid, and show him a modern suspension bridge, and tell him it was built using Euclidean geometry, he would have no idea what you are talking about. Because Euclid started with five postulates and built from there, and later mathematicians continued to build on that. But they were always building, and combining or extending existing principles to deduce new ones. R' Schachter suggested the same with R' Akiva and Moshe - R' Akiva was teaching Torah which was firmly rooted in Toras Moshe, but was advanced by developing the existing framework. Thus, Moshe was consoled when R' Akiva said he knew it from Halacha L'Moshe MiSinai, because he understood that it all was still rooted back to the Torah brought from Har Sinai, and it had not been supplanted or replaced. Thus, everything was told to Moshe, for all of the future chiddushim are not new to the Torah, they are just the complexity and the depth of the Torah being expounded and explicated. But Moshe did not necessarily have the conscious awareness of all of these details of what he was receiving. The Maharal in his Chiddushei Aggados to the Gemara in Menachos, in his second approach, says something similar, namely that Moshe had the השגה of the Torah as a כלל, in one general unified grasp, but not of the particulars. R' Akiva had the grasp of Torah in the form of detailed particulars. (The Maharal understands this to be what it means that R' Akiva was expounding the taggin, the crowns of the letters, which Maharal understands are references to the details which "come out" of the letters.) Perhaps this could mean that Moshe had, in potential, all of the Torah to ever be taught, but not with a conscious appreciation of each detail.
In his first approach the Maharal says something that I don't fully understand but will try to present. Firstly, he established that the taggin represent a level of grasping some higher level, finer concepts of the Torah. He then says that Moshe's level was higher than R' Akiva in that he received everything at the level of prophecy, and everything that he knew, he had higher clarity in because he knew it through prophecy. He also explains that Moshe was on the level of mastery of this world. He therefore knew all of the Torah relevant to this world (which would explain that he knew everything a future scholar would instruct, all of the halachic material of Torah). However, he specifically did not know it through חכמה. R' Akiva knew it through חכמה, and therefore was able to grasp things which are beyond this world, and R' Akiva lived an existence on a level of beyond this world. He could therefore connect to the taggin. (See there for more details and explanation.)