

When they started, they did used to force you to use products edit: aside from their own games(fair cop), some 3rd party games like Lost Planet also required it.
Certain games, and not just valve games, you’d buy in a store and the disc would force you to install and create a steam account to play the single player offline game.
My point is that they did initially to force usage. I’ll edit the post with the game name when I get home.
Edit: Lost Planet. It had a disc but required you to sign up for and use steam to play it.