Microsoft already brought Windows to ARM. Why don't they bring it to RISC V so that more than just Intel and AMD can make CPUs? More competition in the CPU space benefits Microsoft, because when hardware is more compelling, more people will buy it. Or why hasn't anybody bought VIA for their x86 license so they can make laptop/desktop CPUs?
I can't imagine how many resources would be wasted to bring Windows to a platform that nobody uses.