NT is not the majority of windows code though; for windows to be multi architecture, all of windows needs to work with the new architecture; NT, drivers & userspace.
For Linux, if an existing userspace application doesn’t work in aarch64, somebody somewhere will build a port. For windows, so much of their stuff is proprietary that Microsoft are the only ones able to build that port.
Not because “windows bad”, just a consequence of such a locked down system which doesn’t have anything open source to inherit.