I'll point out that GOG has rejected other indie first person dungeon crawlers before. In fact, very few actually get released that aren't classics.
As much as I (and probably a good many other RPGWatch users as well) like the classic Wizardry-style games, they are a niche within a niche within a niche. One that even in the indie game world has only really seen relatively sporadic releases compared to other styles of RPG (including Dungeon Master-style games, which share the same movement and perspective).
I do find their curation to be overly heavy though. There's no legitimate reason to not have many of the rejected titles on there, other than GOG just didn't actually review those games and sent an out of hand rejection notice.
If I ever release my game, I won't even bother submitting it to GOG, that's for certain.