Steam binds game installations to a specific account where you purchased them; and you are not supposed to run that game instal without Steam alongside it, or through another account, or no account at all, or in 2+ computers at the same time. And the way dependencies are handled is part of that.
As such, you can argue that it’s DRM done less worse than most, or that the “DRM-ness” is not its primary “goal”, but you can’t really argue that it doesn’t behave a lot like DRM would, for practical purposes, and for your typical user.