Steam is going to be heavily skewed Nvidia since many games either need it or run poorly without it. Gamers seem to tolerate an otherwise nearly unusable computer for Nvidia graphics acceleration where most users won't.
If there's any strong evidence that NVIDIA still isn't winning in Linux desktop marketshare, I'd certainly be interested to hear it, and it would be news to me. I can imagine Intel technically has a lot of marketshare due to laptops, but then again, Intel and NVIDIA users are hardly mutually exclusive on laptops, either.
I'd pay for things to get better here. I desperately hope that Vulkan as an option for compute can mature and compete with CUDA, but I also think that to do so, quite an ecosystem will need to be built up around it, even if the API and drivers prove sufficient to work as a solid runtime.