WSL – both versions – are MS attempting its age-old "embrace & extend" move.
https://en.wikipedia.org/wiki/Embrace,_extend,_and_extinguis...
I called it a distant relative of the NT POSIX environment and some senior MS bod disagreed and – when I said [[citation needed]] – eventually linked to a bunch of videos and stuff that say that WSL1 is a whole new translation layer and not a kernel personality at all.
Which makes me wonder: why? Do MS not have enough top-flight kernel engineers any more to do an in-kernel version of gvisor? https://github.com/google/gvisor
Others have done it.
Joyent enhanced the old Solaris `lxrun` environment to bring it to 64-bit and kernel 3.x or even 4.x: https://www.slideshare.net/bcantrill/illumos-lx
The FreeBSD Linuxulator does much the same: https://wiki.freebsd.org/Linuxulator