They require steam to be running, don't they?

What happens if steam goes away?

Nope. Adding the "steam has to be running" check is an optional step the game developer performs before they upload their game to steam. The dev can go out of their way to wrap their .exe in the steam DRM.

If the dev does not do this, there is no steam DRM. lots of games dont use it, remember kenshi as an example.

A lot of games on Steam can run without running Steam

It's trivial to bypass that check using a Steam "emulator"

That's not the same as not having DRM

It's like a game only runs on Windows, but also run on Wine

There also often software to strip the drm out of direct purchase games.

The existence of drm removal tools does not make a product drm free, in the same way ms office isn't open source if you steal the source code.

Several run completely fine without Steam running (or even installed)