Update: The developer did change their mind and it's now on GOG for Linux.
What is Supraland? It's a very highly rated first-person action and puzzle game, inspired by the likes of Zelda, Metroid and Portal. It's popular, with an "Overwhelmingly Positive" rating on Steam from over two thousands user reviews and from my time spent in the demo, I can see why as it was pretty sweet.
Speaking in their official Discord server, users questioned the developer to find out about a possible Linux release on GOG, since it's only available for Windows there currently. The reply was a little…unexpected:
Their further comments on it were a little more reasonable and understandable, mostly mentioning lower sales on Linux and again on GOG. Even so, that's a pretty naive and hostile attitude to take towards a store (GOG) and platform (Linux) both of which you only just started supporting.
After speaking to the developer myself, they said it was taken out of context (not that I see how, I followed the whole conversation personally). In reply to the same user who also posted this information on GOG, the developer said:
With the "for the sake of it" comment I was refering to a case of "I will only buy on gog because I want it DRM-free" but it IS DRM-free on Steam since forever. This ignorance and "for the sake of it" attitude made me a little angry.
I have not a single bad thought about gog.
They moved onto saying the Linux version performs poorly compared to the Windows version, saying it's better in Proton (which they also said slightly differently on the GOG forum and here too) so they don't want to give "a version that is inferior for reasons I cannot change". So, they're basically telling people on GOG to use Wine/Proton.
Supra Games are also currently crowdfunding for Supraland 2 on Kickstarter, which is confirmed to be coming to Linux as well.