They can use alternative stores if they want. Its not our fault the alternatves bar gog are shit and anti consumer. Valve is the only one supporting linux so I'm buying my games there to support that effort.
Also steam has a lot more than just the store. The chats, the media sharing, the forums, cloud saves and input profiles. Epic can't even show you a list of games in your library when you log in. I claim the free games each week but ive never even bothered to play them as with steam I can just click play and get on with it. As a long time linux user I value the just works approach and the work that wine and valve have put in.