Why does Steam/Valve care so much about Linux? I know as devs we all would prefer to use Linux/Unix. But developer experience isn’t a good business justification.
They don't want Microsoft to be able to use its control of the OS to push them out. It's not the Valve needs to control the OS, it's that they don't want a company that views them as a competitor to have said control. Linux ensures that they have protection from that.