I see, but there is Steam DRM there. So, I guess as the other commenter was alluding to, if Steam goes belly up so does your collection, regardless of the dev studio's intention (Or atleast, locked behind a DRM bypass).
I understood this in terms of Live Service games, but did not consider Steam's ability to shut down their own platform and kill my locally installed single player games with it (Again, I'm seeing its possible and seems easy to bypass usually, but the principle of the matter)
I tried to search if it's possible for a dev studio to release a game on Steam that works without it, by which I mean that if I uninstall Steam, the games keep working; I wasn't able to confirm, but it seems to be theoretically possible...
None of the games I have in my library work like that, but online some people suggest that some games work even without Steam, once installed.
Your point, however, still stands.