My very brief opinion on that broad question is that they're afraid of being held accountable by their own people. They have power that is tightly held, and introducing more voices leads to greater accountability, which leads to greater transparency, and that is threatening to them.
Why are they not feeling pressure? I think they're feeling pressure from some, and reinforcement and tangible support from others who share their world view and desire.
To the earlier point about networks, they are coordinated and mutually reinforcing, so lots of authoritarian governments are actually, right now, reinforcing each other and providing an alternative form of peer pressure that is actually reinforcing this type of behaviour.