Much like tv/movie streaming platforms
The amount of releases vs legacy games are inversely proportional.
We were always going go reach a point where these sub services were gonna have diminishing returns.
Unless MS/Sony and whoever else in the future constantly gets all the latest releases day 1 (which they won't, it's just not feasible) then these services will all end up making people go "meh" every month than "yaaaay", I mean how many more times can I get limbo for "free"
Pro tip: just sign up for the month when a game you want to play is available then keep your money.