And if you're referring to "Galaxy builds" as "downloadable installers that do not include the Galaxy client", then we're talking about 2 completely different things. I'm talking about a game that is available for Windows on GOG.com which provides Galaxy features such as achievmeents, multiplayer matchmaking etc., but does not ship a Linux build at all on GOG.com due to GOG client and libraries not being available for the Linux platform at this point in time, while they ship both Windows and Linux builds of their game on Steam etc.
The primary difference is whether they want to have Multiplayer features on Linux or not. If that is the case, and those features were implemented using Galaxy, that would definitely be required. But a non-Galaxy port, meaning the same as the Windows non-Galaxy build which doesn't include the multiplayer features, should be just as easy for Linux as any other Linux port. My assumption is that just using a stubbed Galaxy library and removing the multiplayer options from the menu would be 90% of the work in that case.
In my opinion, multiplayer in this game isn't a big part of the draw. Other people may disagree though; I'm not a multiplayer gamer.
That is a level of debate and detail not really up to any of us individual customers and is rather something between the developers of a game and GOG. We can express our opinions about what we'd like to see of course, but they wont necessarily line up with how things actually work in reality behind the scenes.
My comments are reflective expression of actual observation of actual reality insofar as passing the information on to others, rather than taking any sides in a particular debate about such issues. Such debates aren't of interest to me personally, but probably are best served in some other thread however such as one of the "why isn't game XYZ available on GOG for Linux because it is available for Linux on Steam?" threads.