Respectfully, this is bullshit. As mentioned above, the question was about dollars, cents, and optics. Parler costs nothing to cut & there's little PR hit (probably a benefit), Cutting Facebook would cost the platforms money.
The "terms of use violations" or whatever BS they're referencing for booting Parler doesn't even enter into it, the action is based at least 99% on cost/benefit to the platform, not some sanitary inflexible set of rules.
Dorsey showed Twitter's rules mean nothing. Trump violates rules: "oh well he's an exception because he's a head of state [and he's the best thing that ever happened to engagement!]." Trump is losing power & allies are fleeing him: "sure he's still a head of state but this is the exception to the exception, so we're booting him [plus the tides just turned against him and dumping him is more palatable]." Soon we'll have the exception to the exception to the exception.
So let's not play dumb and assert that this is about some fixed set of rules, the tech chiefs are clearly making the rules up as they go along based on "who is in power at the moment, what speech is unpopular at the moment" and above all "what will this cost us in dollars."
And the minute your speech is unpopular (I'm looking at you, anarchists, communists, and libertarians), out the door you go.