Thanks for the information.
I don't understand well why the key cannot be reedemed on GOG instead of Steam then.
The short answer would be because Steam sells a lot more so they figured it's more popular so the CE is Steam. I do agree they need to make money and GOG is not popular enough because all the AAA games fear DRM-free like the plague but hopefully with GOG-Galaxy, GOG can start to really pick up pace and start overtaking Steam. That and Larian is a small team and it seems like supporting multiple digital retailers is a huge pain for them.
Long answer here:
https://www.kickstarter.com/project.../comments?cursor=6958986#comment-6958985
