AFAIK, AMD is not as good as nvidia on Windows. Also because they are less popular, they get less support from program/game developers, which is probably why people are picking nvidia.

I think even if AMD is strictly better than nvidia, it will still take years for nvidia to fall unfortunately. Look at the AMD v.s. intel problem, Intel has been strictly behind AMD for many years now, yet intel still dominates the laptop market, and doing okay in the desktop market.

Obviously, this doesn't mean open-source supporters all need to cave to nvidia. Personally, I will avoid nvidia hardware when I can. But I think we have a long and hard battle ahead of us.