You were never actually able to buy a game, it has always been a "license" to play it. Even for physical cartridges and disks. The difference being, legally speaking, if you actually owned it, you could make and sell copies of it or take the assets from the game and make a new game with them and then sell that. Owning a license means you can play it, but cant make copies or reuse the assets.

Even with physical media, that license could in theory be taken away if the rights holder chose too. Realistically it would be impossible to enforce since there is no way of tracking down all the physical copies, so no one has ever tried to do it. But legally it works exactly the same as on steam. The only change is that a new california law is going to require steam, and other stores, to be transparent about it, but nothing is actually different.

Even on GOG, where they give you a DRM free binary, if the rights holder doesnt want it available anymore, they have to take it away. You wouldn't be able to download it and if you had saved a copy of the DRM free binary, playing it would legally be the same as piracy at that point.

Despite all of this, game preservation is alive and well and isn't going anywhere.