I haven't, as of yet, been able to find an explanation for what Akhenaten did that goes beyond "he was a religious fanatic", but surely there were other reasons?
Previous AMA Egyptian panel section on Akhenaten (please note the issues with the Armana letters)
It was probably down to the fact that control over the elites over the centuries had eroded and it could be that this was an attempt to bring them back under him. By eradicating all the other cults, the priests disappear and the families that promoted them, and so Akhenaten can start with a clean bureaucratic slate. This he does by promoting men loyal to him, and his control over the elites is probably greater than any earlier time. By limiting access to Aten through him and his wife, all cultic observance is controlled by him.
It's hard to be much clearer as after his death, there was a concerted effort to eradicate all mention of him, so the information we have is quite small.
Edit: for the idiot downvote, that's Redford and Assman's position.