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.
And here's a list of games which are sold through Steam but which nonetheless do not use Steam DRM: https://www.pcgamingwiki.com/wiki/The_big_list_of_DRM-free_g...
Why would such a list be necessary if games sold through Steam that used Steam DRM were the minority?