Quote Originally Posted by bankai View Post
Why didnt SS banish aizen to hell?
Hell is a place for degraded human souls and well, Aizen was never a human. Not to mention that the decision about sending someone to hell, doesn't lie within SS's authority (but in Hell's). The verdict is based upon their evil deeds when they were alive and from their degradation to hollow after it ended (you could say that they go to hell, because they were doing no good when they were alive and in their afterlife).