WSL2 essentially invalidates one of the primary design criteria of the NT kernel, which is that the kernel itself should be able to service any number of "personalities" to provide userspace compatibility with other operating systems.

In practice, this turns out to have meant DOS, OS/2, and a barebones POSIX workalike. Modern Linux is too huge and provides useful APIs that go against the grain of modern NT, so applications are slow in WSL1 and there are too many impedance mismatches to paper over to make the investment worth the effort.