Why should they need maintenance? The only maintenance needed is because the OS has zero concern for backwards compatibility.
What do games need? A GL/vulkan context, audio system and user input. They really don't ask for much from the OS itself. It should be able to keep working because it's still doing the same thing. It wasn't broken because it had a bug, but it was broken because Apple decided to break it (and lots of other useful, feature-complete apps). Sometimes, something is just "finished". It shouldn't need "maintaining" to keep running.
I agree. It's not practical to expect apps/games to be maintained forever. People stop working on things. Studios shut down. It's another reason why I think macOS wouldn't work out as a good games platform.