Well, civil rights lawyers have been pretty busy lately trying to stop the slide into facism, so they haven’t gotten around to making our choice of OS a protected class.
Seriously though, why would it be illegal? It’s their game, so they get to be assholes and decide who gets to play it with them. I don’t think that’s ever going to change, and I’m not sure it should. We do the same thing in the Fediverse, deciding who gets to use the instances we control.