Open source on a non open source OS usually sucks, because nearly all open source developers develop for Linux or do multiplatform (web developers, mostly). More money would help, but, if you really are so much into open source that you are developing an open source desktop app, you're unlike to use Windows.
Of course, there are some kinds of open software that are especially bleak even on Linux, but each OS has areas where it is lacking. Anyway, things are getting real better, thanks to gems like the Steam client, Blender, or Godot.