Last year Trump and team were collecting evidence of FB and Twtr censoring, and I'm thinking upper management was served with indictments, or, the company was put on notice that they would be treated as publishers and not facilitators if they continued their practices, or maybe a bit of both.  I suspect both. Some other options - the military breached the company firewalls and basically took over, Darpa has been cleaned out, and they took back control of their algorithms and FB has been walled off.  But that would be more draconian, and that seems unlikely to me.  Except for Darpa being cleaned out.  That could have happened without anyone noticing.