Gog literally won’t allow you to sell a game if it has DRM

So, Steam respects their customers enough to offer them a choice while GOG doesn't; good to know.

set whatever environment variables the game needs, create the necessary folders, install the redistributable runtimes the game needs to run,and link the dlls properly

Ok, and? I can do all that on Steam too. I can even launch the game directly without involving Steam at all.

If you only have the game files you have to manage all of that yourself

Yeah, and all that is a huge pain in the ass. Having it to do myself isn't a positive.