Regarding Twitter, Elon seems to like trial and error, right? That's how SpaceX developed their rockets - by trying new things and testing them frequently, to see if they work.
So with Twitter I think he's just trying to see what he can get away with. And if he can't get away with something then he'll just roll it back.
As for Reddit, I guess they saw Twitter trying to squeeze more money from their platform and thought "let's try that too".
Twitter had experimented and had a fair system in place through previous trial and error. Elon thought it wasn't good enough and then ran into the wall face-first thinking he was smarter than the average guy. Spoiler: he wasn't.