Hardware support is always a big issue with a new OS designed to be run directly, it is much easier for a new OS to start the other way as a VM run by a more mature OS. Getting qemu working is also quite a bit of work, although Xen Dom0 support would be easier. There are security implications of the hosting implemention as well. However, long term a general purpose OS will almost certainly want to support VMs so the extra work to do a WSL2-style integration is less than trying to keep up with the large number of complex Linux system calls for direct binary compatability and there are also major security implications to doing things that way.