
Marketshare, and you have to remember the difference between platform and store. If Epic made them exclusive to the Epic Machine™ then there would be a problem but moving from Steam to Epic doesn’t remove Windows support.
Imagine Target bought Great Value (Walmart brand) and moved it from Walmart to target. Would anyone care?

All things that should and are handled by different companies.
Steam violates Unix philosophy so it should never be on a Linux system.
Even their Wine fork requires the Steam runtime.
Also you know you’re lying when you boast about Steam support.
It can be a store, a launcher, a compatibility later, a discussion board, a social platform, a download host, a game developer, or an input manager but it cannot be all those at once.
Epic isn’t without fault either, they also do more than just Unreal Engine. But no one can argue they are worse/do more than Steam and their Linux support better.
Yeah, glasses houses and such it’s odd for Valve to comment on this.