But to answer the thread topic seriously: The whole purpose of this story is to show that love and cooperation with others is the right way to do things, and that's what the Senju Clan and all those related to them represent. After all, the "Will of Fire" started with Hashirama unless I am mistaken. The issue is that most of the Uchihas strayed from those ideals at some point. Obito redeemed himself, but then died straight after.(plus he had committed far too many crimes). Madara probably realised that he was wrong in the end when chatting with Hashirama, but he was obviously far too late. Sasuke got himself redeemed properly/pardoned, and probably lived a nice life, but Kakashi and Naruto are obvious choices for Hokage above him.(the former due to his experience at the time, and the latter due to striving for that goal as a kid plus never straying from his ideals.) As for Itachi, whilst you could argue that he had the WOF, he found himself in tragic circumstances which lead to the UM. Can't exactly have him as hokage, since the whole thing had to be hushed up. So, none of the Uchihas could be the Hokage within the story, due to the circumstances surrounding them.