Besides what the other person said, there's also the whole treating Linux users as second class citizens. If they didn't had a launcher for Windows, then it wouldn't be that big of a problem, but the fact that they did created a launcher for Windows years ago and porting it to Linux has been the most upvoted feature request since then and they haven't done it is a slap in the face of a community that shares a lot of their beliefs. Valve is investing money on making Linux gaming a reality, GoG won't even port their launcher to Linux, despite not caring for a launcher I know who I'm giving my money.