There would be many devs out there, big and small, and I doubt it is realistic for GOG to discover and court them all.

What GOG need to rely on and focus on is promotion. Take out adverts on Steam. LOL
Or more realistically, at places where gamers get news about games. How many gamers do that outside of Steam, I don't know, and I'd imagine that any real keen gamer would have heard about GOG by now. The promotions on Amazon Prime are certainly a good way to go.

If I was advising GOG, I would advise them doing a really good documentary about DRM and DRM-Free, and maybe not just about in games, but overall. Get people thinking and pondering about DRM.

I don't know if GOG has ever done a full list on achievements since they started, but that could also be a great promotion for when people start to check them out.

And as they say, even some bad promotion is better than no promotion. People can often remember a name, but not necessarily any detail in relation to it, except it involves games. I'm not actually sure that GOG is necessarily a great name, but maybe it is if promoted right. Maybe GROG would work better ... LOL.

I bet a lot of folk discovered about GOG for the first time, during the Devotion debacle, and while a certain percentage of them were negative, not all would have been, and maybe some of the negative eventually changed to positive.