Right now it's open to anyone who pre-ordered or anyone who has game pass. it's open to everyone for free next week. maybe they should have called it limited instead of open, but it isn't closed to anyone, anyone can get game pass and play the beta rn so it is technically an open beta.
and why are people playing CoD? because it's really solid gameplay that recieves weekly updates and events to always keep things fresh. the new movement system in this one is really a game changer and makes the game a lot of fun to play.
it works surprisingly great on a controller