You probably aren't the target market for Steam in that case.
If there was a compelling collection of open source games I would certainly play them but that has never really been the case.
There are tangible advantages in having open source tools and components such as compilers,kernels and desktop environments even without every program on the system being open source.
I would not consider GNU/Linux users the target market either. I would consider the target market to be Windows users that don't want to use Windows for whatever reason. These people don't care what they use as long as it isn't Windows, they aren't loyal to any one system for any particular reason.
Personally I do not derive pleasure from just playing games, I need to be able to study their source code and modify them. So I see no advantages in having proprietary games on my system. I hope that other GNU/Linux users acknowledge this as well. The one true value of the system is that it is GPL-ed.
I'm not sure what the difference is between a GNU/Linux user and a person who is using GNU/Linux because they don't want to use Windows.
If you look at places like /r/linux on reddit the Linux fanboys there are practically wetting themselves over steam.
I agree that more open source games would be a good thing, but I don't see it as necessarily more important than having access to the unedited recordings of a piece of music.
Is someone really a GNU/Linux user if they have no respect for the core values of the system? I personally don't understand the exuberance on reddit. It's just another package manager in the already large sea of them, and a proprietary DRMed one at that; it doesn't really seem to provide any practical advantages to anybody. I believe it did on Windows, where even developers didn't have any reasonable package management system until a few years ago. But I see no real business strategy here. Also funny that you mention that because as a hobbyist musician I think it would be pretty cool to have CC-SA'ed masters of some of my favorite songs.
If there was a compelling collection of open source games I would certainly play them but that has never really been the case.
There are tangible advantages in having open source tools and components such as compilers,kernels and desktop environments even without every program on the system being open source.