The whole reason Steam exists is because Valve pushed it with high-profile content, over a decade ago - initially Half-Life multiplayer (To a ton of community backlash), followed by Half-Life 2, as Steam exclusives.

It's only been the past several years that Valve has completely stopped making games, and started working on other things.

I would guess it took quite a shift for the Valve of today to make Alyx. I barely even think of them as a game dev anymore.

There was the Orange Box, which was an absolutely fantastic deal: https://en.wikipedia.org/wiki/The_Orange_Box