Oh, yeah. Last time I checked Linux was really bad at binary compatibility. Perhaps they have made improvements since then, but it makes it difficult on hardware manufacturers who don't want to open source their drivers. Nvidia and AMD don't want to do that because drivers are trade secrets, both revealing stuff about their hardware that they don't readily share and providing some competitive advantage. A GPU is basically just a big SIMD engine. I'm not super into graphics, so pardon if I speak imprecisely, but my understanding is the software that sits between the compute an engine and the OS, taking DX/OGL calls and actually causing the hardware to effect them is nontrivial. And the GPU vendors would like to keep their work on that as proprietary product, even though they don't charge for the software.