It’s because Epic bought the Rocket League devs, Psyonix, in 2019. In 2020, they pulled it from Steam, to drive traffic to the Epic store. And yes, it’s also free to play now, but you still can’t get it on Steam, unless you bought it there before they pulled it. If you did, it still works fine on Steam today.
in fact for the games that have been removed I actually still have full access, like rocket League still in my library just not purchasable anymore
Isn’t that just because RL went free to play?
It’s because Epic bought the Rocket League devs, Psyonix, in 2019. In 2020, they pulled it from Steam, to drive traffic to the Epic store. And yes, it’s also free to play now, but you still can’t get it on Steam, unless you bought it there before they pulled it. If you did, it still works fine on Steam today.