toxicTom: I do think for games that are not no-brainers to list, the subjective tastes of the curators do play a bigger role than they would probably admit.
And also GOG have sometimes justified rejections based on what they thought the audience would not be interested in.
And they later had to admit they were wrong :-)
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Once again, great response.
Curation certainly wouldn't be an exact science, and like you say, probably effected by the odd bias.
I am sure there are more factors than those you and I and others have already listed.
I think reputation of provider was mentioned, and of course that could come from a variety of sources.
GOG seemingly avoid controversy etc if they can, and so probably just politely refuse a provider, without necessarily saying the real reason why.
There are certainly some game providers here, who don't appear to provide their product here with good intentions. Just an ultimate lure to buy (again even) at Steam due to frustration.
We have incomplete games, that are quite telling when more advanced versions, sometimes complete versions are available elsewhere. Bugfix updates are missing in many cases, that do exist on Steam etc.
GOG rarely ever seem to bother defending themselves, which can of course look bad in the eyes of some, whose imagination runs riot, always assuming the worst. Look at the ridiculous over-reaction by a good many about the Devotion game, and people are still posting about it. I'm even beyond rolling my eyes now ... just mild background noise.
It doesn't make sense to alienate providers or customers, but sometimes I guess it can't be helped. At the end of the day, GOG are a store that wants to survive, and from what I have seen, will try to stick as close to its DRM-Free mantra as it feasibly can, while still providing great games. Clearly with MP for instance, it isn't always possible.
GOG are on a journey.
Providers are on a journey with GOG.
Customers are on a journey here with both.
Where we will end up eventually, is anyone's guess.
I don't attribute deliberate ill intent by GOG, just possibly bad decision making sometimes or market forces and survival. At the end of the day, all the GOG personnel are human just like the rest of us. So mistakes happen and shit happens, and flaws exist that can be taken advantage of. Misunderstandings are in abundance. None of us are perfect, and some of us live in glass houses.