Rebranding Twitter - without a great deal of thought and planning - is as dumb as rocks. The Twitter brand isn't irrevocably toxic (yet): it's actually quite evocative of the way the platform functions, and so on. He's also not the CEO any more, so it shouldn't even be his decision. Depending on the contracts he signed to secure external finance for the deal, there's even the possibility that his creditors could force him to step away from the company if they felt he was damaging it and thus their investment.
I think his ego probably has a lot to do with it - even if just the fact he's mad as hell he colossally fucked up and bought it at an overpriced sum, and has only managed to make it even worse. Changing its name doesn't change those facts, but he possibly now associates the name with his exquisitely painful and public embarrassment, and this is one way to not hear it any more.