They’ve never successfully built up a non-x86 userbase on Windows.
An architecture switch where a lot of software won’t run well (or at all) is a big risk for them that people could start to go elsewhere in non-trivial numbers.
Apple, Linux, Chromebook.
Yes they have a compatibility layer for running x86 on ARM. They could make it for other archs. But that’s still a big effort and consumers may not trust.