I'm pretty sure idealogically valve are opposed to locking people into their ecosystem. They don't even make it so you can only play their own games with steam, and they allow you to add non-steam games to your library. They're a weird comapny in general, they have a pretty hardcore horizontal management system going on in their company which as I understand as an outsider is a big reason why they've struggled to bring stuff to market of late.
Their (leaked) employee handbook is literally subtitled "A fearless adventure in knowing what to do when no one’s there telling you what to do"
I mean that even if steam closed tomorrow, you would be able to play all your games. They're literally just installed in a folder on your computer and steam clicks the exe for you. They also released server code for most of their own games so you can run your own. Most companies would have gated access to their servers so you could only run the game when you could connect to their database
Their (leaked) employee handbook is literally subtitled "A fearless adventure in knowing what to do when no one’s there telling you what to do"