Interesting Facts. In my opinion the market for games that are focused only on windows. But Linux has shown a promising platform.
The market has changed and not only overnight. There are more and more mobile stuff for your smartphone, and the new Steam console are bundled with Linux, over 200+ known games are official for Linux right now. I think it's the market of the future, as we can see it's more the coding aspect than the OS. Imho, OpenGL is the features, and this works on any OS not only Windows. It's up to the developer if he choose to porting it to other OS than Windows or not. But I agree that the market for windows is bigger than for Linux, we only can hope this will be changed in the near future.
In the near future? I find that unlikely. Cash is king in programming / games. Microsoft has collaborated with Directx and all games run on it. But maybe in five years maybe Linux gain strength to break it.
Linux have the OpenGL ready and working as should. OpenGL is the native engine for graphics on Android. DirectX will not be the 'boss' on this mobile times.