There's nothing really comparable between calling for someone's assassination, and on the other hand, someone to be arrested and brought to justice for a crime.
And there's also the fact that there's no basis in reality for the claims to be begin with.
In all of this confusion, it is true that Parler was essentially (Edit: not! obviously 'not' moderated)moderated - and - there was a lot of really terrible stuff happening there. Like 'kill these people'. The cover that Twitter can use is that they actual do moderate people and try to get rid of them. Mostly.
Parler must have had a huge leadership failure to play that game and think they were going to get away with it. There is zero chance that hosting people directly calling for violence, unmoderated, is going to last when associated with other people's brands.
I believe the CEO actually wanted to do something but his backers didn't.