I wanted to buy this game called Prominence so I sent an email to the developer and asked them if they could make the game available for purchase on GOG. They replied and told me that they had tried to put the game here but GOG declined.

I'm having trouble understanding why GOG would decline any game, unless there was something morally objectionable about it, such as being pornographic or some such thing.

My logical mind tells me: more games equals more profits. Am I missing something?

I see three reasons mainly why they decline a game :
1 GOG support their game with all associated costs (cost with the testing of GOG installers and GOG galaxy, of the supported OSes, of the support for players and all languages associated with it). GOG has around 150 employees to support, it's not itchio.
2 GOG is a curated store. Contrary to steam they believe games have to be of a certain quality to be sold here (I don't know Prominence and if it's the reason why, just saying).
3 GOG sells around up to 15% of what steam sells for a game that release at the same time on steam and GOG. If games sell too few overall, it's just not worth it for them.

Sometime back, a GOG staff, a blue, mentioned something about talking a little more in-depth about what goes into the decision-making process for the titles that make it here. That has kind of fallen through unfortunately. But my belief is that, there is obviously data that we are not seeing since we are not privy to it. And even though we do justly complain, it's hard to claim that it's an objective point either without this.

Yes. You miss the expenses of maintaining the game and it's community. And it's not just a question of "technical" maintanance, but also watching over the controversial content. Just look at Steam - people constantly critisize it for having a ton of garbage titles and its forums to be toxic. Of course, its always a very subjective point of view - what is really harmful and inappropriate and what is only seen as such by sanctimonious mob of hyporcites. But apparently GOG thiks its better safe than sorry.

Except that GOG has rejected many really good games which would fit perfectly here (Aeon of Sands as a recent example), at the same time as accepting some real garbage. Just look at all the indie games with terrible artwork that are accepted here just because they seem to be trendy.

Releasing a game on the (GOG) store means expenses too to GOG. Marketing, support to customers, taking care of the offline installers, keeping in touch with the developers (support for developers, or demanding them to release the same updates on GOG as they do on Steam, etc.) and so on and so forth, you know the drill don't you, huh? Huh?

So GOG must believe the game would sell well enough to compensate for all those things above, and leave profit to GOG too. Otherwise it doesn't make that much sense to release the game on GOG.

Also, in many cases it might simply be that the game is offered to GOG at an inconvenient time, like GOG is already swamped with lots of other releases at the same time, especially other similar games as the game being offered. So it might not be only about what, but also when. Is there some list of these REALLY good games that GOG has rejected, so that I can give a final verdict whether they really are any good?

Since it is GOG's business, I presume GOG staff sees better what kind of stuff sells on GOG, rather than us mere mortals. Maybe the earlier "really good games" from the same developer failed to sell on GOG, for a reason or another.

I can give you a few names that I liked, but just because I liked them and would rather they came here over some other games that GOG has released doesn't mean you will think the same way. And for that reason alone its not really a final vertict your giving, just your opinion.

But anyway Barry has posted a thread about GOG's declined games.

And from that list the ones I have played and liked are AR-K (The Great Escape was alright), Deathsmiles, Her Majesty's Spiffing, Jim Power, Penny Arcade & Pushover.

Bulletwitch was also declined from GOG which I would of also brought here given the chance.

Alot of GOG's cruation comes across to me as a user about being more about whoever is judging a game and if they like it opposed to if it will sell well. And also what the current trend is. For example the moment it's indie games and we are seeing alot of them released here.

Because they don't have a system in place that can release every single game. As a result, they must choose which games to release/prioritize and decline/delay the rest.

This. You can dress it up any way you like but *every* store except a few of the massive ones 'curates' their store out of necessity, for the simple fact that they simply can not release that many games. Even Steam was not capable of releasing a larger number of games till they did an entire do-over of their system (shortly before the flood), they simply weren't capable of it (they explained this on a dev days video). And this is Steam, which had already focused on letting the devs do more and more things on their own.

GOG is simply nowhere close to that yet, so they have to pick and chose. Almost every store does this. Steam's one of the few to have reached a point where they have the luxury of simply adding more games. Which means for them, they didn't have to make the decision anymore which games they thought were most likely to make more money. At that point, for Steam, more games = more money.

Of course, it wasn't quite that simple and while it appears to have led to more profitability it also introduced a whole new set of problems (discoverability mostly). Ideally, if/when GOG ever reaches that point they won't reinvent the wheel and instead pick up where Steam has already improved by then.

No list, but there are (a) few instances where good titles were indeed rejected. Ion Maiden was initially turned down and later accepted when they saw the buzz around it on Steam.

Yeah that post isn't coming anymore, sorry. There's a draft on Google docs somewhere but hey, maybe someone will take up the idea in the future, hopefully.

Yeah I am aware of that list, but I wasn't looking for a list of all games GOG has allegedly rejected for a reason or another, but the really great ones.

I quickly checked the games you mentioned on Steam for reviews, as well as the game in the first message. Most seemed to have "mixed" or "mostly positive" reviews, so I got an impression they are "ok" at best. Also there was no data how well they have sold on Steam.

We don't always know all the reasons for rejection. For instance, it might be some developer wants to add some DRM of their own to the game, or isn't willing to add achievements to the GOG version. I don't care for achievements, but unfortunately many nowadays seem to (e.g. in the "games that treat GOG customers as second class citizens"-discussion many are already mentioning games missing mere achievements. So, maybe GOG nowadays feels they can't add such games either.

I'm not justifying their decisions. How could I know why they took them ?

I don't use steam, and some games sound interesting to me like The Quest, Das Geisterschiff or At The gates, but all of those have been rejected by GOG because of "Reasons". And that's absolutely normal, a business will always have reasons to draw a line somewhere on their expenses.

As for those famous trendy shitty indie games you don't like, a tiny handfull of games get removed each year of the store because they didn't sell and the pub or dev are butthurt. That's the only criteria GOG will have about regretting to have taken them, because they lost some monies on them, wether we like their artwork or not.

I'm still very happy they accepted Telepath Tactics or the Braveland series which must not have sold really well, but are still there.

¾ the time someone whinges about a game that GOG has "overlooked" or "rejected" it often is a game I've well never heard of.

Does that say something about the games or does it say more about you though?