I think the GP means because the game is a time sink, but you raise an interesting point. I wanted to say "that'll never happen", but someone could fork Linux, add DRM, and then that becomes massively popular and we're done.
Realistically, that's only going to happen if Valve, specifically, decides to do it. There isn't really another player in the linux-gaming business with enough skin in the game to make it worthwhile.
I could imagine Epic Games trying to keep the Epic Games Store relevant by making a SteamOS competitor, with the idea of attracting developers with strong kernel-level DRM and anti-cheat
