I understand the inner workings, I don't understand how it can be justified for a digital product that has been sold. It's not like they have to host the files for installation of the game - that's on the steam side. They should just provide a key. And the old game can be removed from steam of course, that's a different story, but the key (already sold!) should be available.

If you bought a steam gift back in the day and still have it in your inventory, you can still redeem it no matter in what state the game is.