

This.
What eventually kills these platforms is “death by thousand cuts”. Enshitification, controversies, legal problems will alienate users bit by bit. Competing services will then make some people visit less and less until they stop coming at all.
These platforms are competing for peoples attention/time which is finite resource.


For my understanding its up to Valve to handle support for Windows unless you mean releasing games on steam. Attempts to block Steam would probably violate anti-trust laws and cause massive PR backlash.