From the opinion piece:
Last year, I pointed out how many big publishers came crawlin’ back to Steam after trying their own things: EA, Activision, Microsoft. This year, for the first time ever, two Blizzard games released on Steam: Overwatch and Diablo 4.



There is nothing exclusive to steam with respect to Linux support. All of the things required for games to run on Linux which valve support are fully open source and even existed before valve got involved. They just threw money at the efforts and turbo charged it (which is great).
Yes, which makes it even more puzzling that the competitors don’t even try to capitalize on the success of Steam Deck and publish their own store on Flathub, utilizing the very same FOSS technologies to make the games run.