The impeachments failed to find any guilt.
He was exonerated.
If he was banned for the same reason, that would then be criminal, since the impeachments were found to be groundless.
Inciting violence is not against any terms of agreement with any company.
For example, if you post that Somali pirates should be blown up with drones or that rapists should be castrated, that is not at all illegal or any violation of terms.
And Twitter does not get to be the arbitrary decider.
It has to be decided in court, otherwise it is a 1st amendment violation.
If you can not prosecute Trump, then it is illegal to censor that which can not be prosecuted.