They’ve made Linux gaming a thing. And there where no players there either. So I do not believe that is their actual reason.
The actual reason is that Valve does not want to be beholden or locked to a corporate entity like Apple or Microsoft. They would be very dependent on the whims of those companies.
Linux gives them a platform where they know and can influence it’s future.
Please keep your faith to yourself, we have too many as it is.