Facebook, allegedly, has an "army" of moderators. Parler, on the other hand, relied on voluntary "flagging", and they admitted (quoted in some other article from today), that they had a backlog of some 26,000 posts to review. So, while this stuff looks arbitrary on the surface, I guess we will just have to see what comes out in discovery in these lawsuits and what happens with judge and jury.
Parler has allegedly had hundreds of paid moderators for months. They also allegedly cleared their backlog over the weekend in a foolish belief they could be on the right side of AWS politics.
Same reason tech firms are happy to "stand up" for democracy in small developing nations but won't say boo to China.
If you're looking to big business for some consistent moral principle, you're looking in the wrong place.