It also does its best to control the experience end-to-end to make sure no one can innovate their way out of these algorithmic feeds and ads. People aren't building better client apps because they fear getting sued. Imagine using Facebook but doing so via a comfortable UI that puts you first, gives you complete control, and allows you stuff like cross-posting to other services. This is their nightmare.
And another problem: the US government is on their side from what I see happening (disclaimer: I'm not from US). It should be such that if they do try to sue you over a browser extension or an unofficial app or whatever, they would get laughed out of the court because you were in your right to do what you did. But unfortunately, there are apparently laws that do allow them to sue people trying to improve their own user experience on someone else's online service.