People have only so much time in their lives. No one acts on perfect information; decision-making is a recursive process where you find a quantum of info about an issue and make a quantum sub-decision whether to arrive at a definite verdict right now or research moar. "This game was rejected by GOG" is one such piece of info, and it isn't good for the game's prospects. You as a hobbyist player can independently decide to allocate some time to independently verify the game's quality once the game has been brought to your attention via a personal channel; a professional cannot afford to do this for every game evar.

Data mining, automating and dehumanizing data handling has been a contentious issue just about everywhere, and that self-perpetuating shit can completely crash a person's life through a net of automated positive feedback unbroken by actual independent human eyes. In the same way, it can hurt a game's chances of success and the dev's chance of sustaining a business. If you're unemployed and have had no luck finding work, the longer you stay unemployed, the less likely you are to get a job any time soon, because employers start thinking there must be something wrong with you and won't give you the time of their day to prove otherwise in person. If your application for a loan is rejected by a bank (for example, because you found out about the scammy opt-out hidden fees and opted out), the bank can shit on your profile and get you blacklisted by other banks.

GOG's rejection list is markedly different from a random internet user's list of games they didn't like. Because you're a player and looking for highly subjective fun; GOG is a business and their main criterion is profits for their business, which is substantially less subjective: every other business is also on the lookout for profits. Sure, a game's success might vary between services, but it is bound to correlate WAY more than your tastes and my tastes. Your proposed rejection list might as well be titled "here be bad games and/or difficult people we consider unprofitable to collaborate with".

Even the effectiveness of a hypothetical hidden rejection list which is nevertheless open to "the community" would be nil. GOG has an internal curation process which is evidently working; user votes are already a factor, as GOG has stated multiple times. GOG isn't ideologically driven; they want profits, they go DRM-free because it's a profitable niche, and it's in their best interest to sell games they think are going to sell well. "Rescuing" a rejected title through voting would be, best case, a grassroots campaign at least partially influenced by ill will toward GOG, it isn't good for business by any stretch of the imagination and GOG has no reason whatsoever to officially trigger it.

Yes, it's probably frustrating to find out a game you were interested in and wanted to buy here was rejected -- everyone, tautologically, likes the games they think are good. But every other user has their own opinion obn what exactly is good, and when you leave it to popular voting, you have Greenlight. And lo and behold, the GOG forum community doesn't actually like Greenlight and the results it outputs. Every single user in the forums [naturally, tautologically] thinks things would be better if GOG agreed with them personally, but we as a community vote against decision-making by popular vote.