GOG only started a few months ago to add Linux versions. They started with a smaller range of games to guarantee their support quality. GOG stated, that they're increasing the number of Linux games till the end of the year. There's no statement on which game's Linux versions will be added next, but there's a good chance that the Indie titles with already existing and working Linux versions won't take to long to be available.

I understand and have hope for more linux games on GOG.

What with the arrival of the second season, I hope there'll be a Linux version to go with the first!

I actually have problems running the Linux version of The Last Door Season 1, so I run the Windows version via Wine instead. Humble has the Linux version... I haven't been able to get it to work. If you really want to play it you can set it up in Wine, you should only need Adobe Air, and possibly the full setup of Direct X.

My assumption is that GOG hasn't included the Linux version due to problems running it. Just a guess though..