The final-straw tweets were after the riots had subsided, and were largely innocuous. But Twitter cited that they were being interpreted (as evidenced by replies) as calling for violence. For example, a tweet that said "I will not be at the inauguration" was interpreted as "If you attack the inauguration I won't be harmed."

So it's not so much a case where something finally crossed the line. And if you look just at the removed content you'd say "I don't see the big deal". It's more the pattern: the sum total of what he said was interpreted as calling for violence -- not reading into it by outsiders, but in the actions and the words of the people taking them. YouTube, Twitter, and others don't want to be in the spotlight if future communications are interpreted that way.

If there hadn't been violence, he'd still be on these media. But there has been, and what changes suddenly is that people who said "These will cause violence" now say "These did cause violence, and there will be more if you don't do something before rather than after the fact".

The content that was removed is readily available if you'd like to read it, but you'll find it underwhelming.