“All of this work is broadly applicable to the PC platform, and it’s going to continue to expand over time. Supporting multiple platforms, multiple chipsets, controllers for different machines that are out there and even ones that aren’t out yet.”
[…] Valve’s goal with the OS is to have it compatible with traditional PCs, laptops, portable consoles and any other formats.
Or, like their entire business model for the last decade or two, they’re focused on competing at a service level rather than trying to push everyone out of the market by force.
Microsoft has made sure to make their library of games available on Steam for a reason. They know they can’t… or won’t compete at a service level.