They banned him because he refused to attend Biden's inauguration. I posted a link to @TwitterSafety earlier where they openly admitted this. Trump did not tell people to go out and be violent, if he did, he deserves the ban.
Context matters. Sure he didn't tell them "go and kill a cop at the Capitol" but he did tell them to go there and disrupt the proceedings and it resulted in violence. It's disingenuous to deny that Trump's rhetoric is inciting violence. And he is not backing down from the underlying false claims of election fraud, which is what encourages his supporters to be violent.
I'm not defending Twitter in any way - I think their whole system is thoroughly fucked since it's basically a trolling platform - but Trump doesn't have any plausible argument in this dispute. If he's too obnoxious even for Twitter that's entirely his problem.