Technically WSL1 is superior, sure, but is that what users want? Seems like users are happily using VMs to run Docker on Mac and many don't even know it is VM underneath. I suppose max compatibility with Linux kernel is more of a desirable behavior, plus the engineering cost of WSL2 is minuscule compared to WSL1, especially once it is done. WSL1 would require continuous reimplementation of complex Linux kernel features as Windows syscalls.