With the exception that the Windows Subsystem for Linux can just rely on the opensource glibc et al. So, they basically 'only'[1] have to implement the syscall interface of the Linux kernel. They do not have to do any work to reimplement all the core Linux libraries in a compatible way.

Wine has a much harder task. Since the common Windows libraries are closed source and non-redistributable, the Wine project basically has to reimplement every API/ABI that Windows provides. This is a much larger and harder project.

It would be a nice gesture of Microsoft if they released some of the core Windows libraries as open source. But of course, that's not going to happen.

[1] This is of course much harder than it sounds.