Their anti-DRM stance is arguably their only compelling feature as opposed to just buying steam.
I remember the old game launcher that was called Desura?, which a lot of those third-party keys sites would sell keys for, and it's no longer around. So one of the main concerns with these online platforms is them disappearing and losing all your stuff.
Quite frankly, I am happy that GOG exists for this niche. It would be less "sabotaging" if consumers would actually vote in their own interests. However, this has been shown time and time again to never happen, sadly.