Many/most Steam games use Steam servers to authenticate ownership. It's a store, but it's also a DRM provider. Many games would require cracking to keep working.
Can you be more specific or offer any evidence? That Valve offers DRM through Steam is unambiguously true. Here's their developer document on it: https://partner.steamgames.com/doc/features/drm
Any game using Steamworks behaves this way, which is a pretty massive chunk of them. Ubisoft uses their own DRM which is an entirely different system.
I think what you may be saying is the behavior if you open a Steamworks game while Steam is opened, it just executes as normal. Any authentication or nonsense happens in the background. Try opening a Steamworks game with steam closed, it will force steam to open and login before the game can be played.
You can test this. Delete steam, restart your computer and launch a title.
You'll get a message about steam.dll missing or being unable to authenticate.
You can also sign out of steam, unplug from the internet and try to launch - and again, you won't be able to except this time steam will launch and tell you to login.
That's always just been a wishful statement of intent with no legal backing. Valve might be unable or unwilling to actually follow through on that urban legend if they do ever shut down for some reason.
Not true. Maybe if you mainly play ubisoft tiles.