It's not what happened and it has nothing to do with Facebook or twitter employees (who have almost zero power, they haven't even unionized yet!).
Facebook or Twitter could have banned Trump & al. for content policy violation years ago (and they probably should have actually, because you know, policy violation) but they did not because conservatives were in charge and then had power to retaliate. Now they are banning them now, because now the democrats are in charge, and they are definitely going to retaliate hadn't social network ban Trump.
American social networks will do things which don't annoy the American government too much, so it leave them alone. What's happening here, is European govts wanting the same level of power than the US one.