That may be a factor but I think it's pretty easy to see why banning him now (instead of earlier) could be done without the reasons you invoked: 1. His tweets

That may be a factor but I think it's pretty easy to see why banning him now (instead of earlier) could be done without the reasons you invoked: 1. His tweets didn't incite angry mobs to assault federal buildings before 2. Some time ago when Twitter was defending why they aren't banning his account, they said something about this effectively being a public government account so banning it would do more bad than good (and instead Twitter went ahead and "annotated" his tweets instead of just removing them). This determination had both pros and cons for Trump, the pro being much harder to ban his account but the con being that he couldn't block people from replying to his tweets anymore. With him now out of office his account loses that status so it should be much easier to ban it.