They did bend their own rules. But not because they are all card carrying Democrats. They did it because they couldn't stand having the person that very obviously instigated Jan 6th on the platform anymore.
It took a mob (following, supporting, assembled, and whipped up by Trump) storming the capital building to get them to boot Trump. I don't see how you get from there to 'political differences'. If that was the case he would have been gone much sooner.
Problem was that he didn't do it (entirely) by tweet. So they found an excuse. That much is true.