ChrisGriffin: And by older releases I don't mean games from 10+ years ago, but the games that have been recently released on different platforms, but not on GOG.
Examples include: Ittle Dew 2, Celeste, The Binding Of Isaac: Rebirth, Monument Valley, Axiom Verge and many other recent titles.
So quite recent games which for whatever reason were not initially released on GOG, but were released on other PC platforms.
I know that each case should be considered individually, but for some reason most recent games don't find it's way to GOG. Maybe there's a common reason?
It's hard to say since the details are often almost usually vague (and I don't know for certain if it's because of NDA), but there are usually two reasons that I've seen in my experience here:
a)
GOG doesn't want the game: These are often on the grounds that are vague and unclear, under circumstances that are usually related second- or third-hand. We saw this in the case of games like The Cat Lady and Braid. In the case of the latter, there were almost no details given (AFAIK) but speculation revolved around the fact that the game had been featured multiple times in bundles and discounts before. People speculated that GOG saw no clear business case for offering and supporting it for sale. In the case of the former, I don't fully recall the details but from what I recall someone on the forums related that GOG rejected it on the grounds that it wasn't a good fit for their catalogue.
In both cases, a large upswell of user responses later convinced GOG to put them up for sale.
Recently we saw the case of Zachtronic's Magnum Opus, which allegedly was rejected on the grounds of it seeming too much like a mobile game. After another upswell of user support, and even coverage on Kotaku, GOG also put it up for sale.
Other games (like Starward Rogue, a particular sore point for me) remain off the catalogue even though the developer has almost all of their games already for sale on GOG.
b)
The developers don't want it on GOG: Some of the reasons I've seen pop up on the forums for this are (a) the developers leverage features/functionality in the Steam APIs/infrastructure that can't be easily replicated by Galaxy or other non-Steam means, (b) the developers find the update process for GOG too difficult compared to Steam, and (c) their development workflow necessitated GOG representing a third version of their game, which they don't have the resources to maintain and support, or (d) all of the above.
We saw this with one InDev game (I can't rightly recall the name at the moment), where the developers have stated on the forums that their wasn't a compelling business case for them to devote resources to supporting and developing a GOG build of their game. Others have allegedly voiced problems with GOG's developer relations and update process, through emails to forum members or posts on Twitter.
Either way the best thing you could do is take to social media/email/etc. and pester both the developer and GOG to offer the game here. Once enough people do so, perhaps both parties can see a convincing business case to make a deal with each other.