They can't allow you to download Linux versions without also being responsible for those versions, and the support team isn't ready for that yet. To paraphrase a recent TET comment, they simply aren't willing to just throw up some random tarballs and say "GOOD LUCK!" When they start supporting Linux, they're going to do it right.
Why? I mean why can't they allow us to download Linux versions without taking responsibility for it?
Linux users are used to getting sh*t thrown in their faces if they want to play games anyway, so Linux people usually help themselves instead of b*tching without end about something not working. So if there is a Linux version made from a game, GoG could simply let us download it as an extra, instead of making a big fuss of it, like with Mac versions.
I love GoG, but it is a bit insulting that one has to play around and suffer with a legally bought game in wine, if there is a Linux version is available.