(there's a bit of history there - a company developed it for a commercial product, Google ended up forking the open source parts for the android emulator which eventually resulted in them contributing it back to qemu upstream).
I worry if there is a hypervisor implementation monoculture where everybody is wrapping the same kernel interface, we lose some possibility for a better implementation.
Or if some problem of the future, not VMs, some day requires kernel hacking, but this is artificially locked out. Apple is choosing to not have that innovation happen on their platform. Seems short sighted.
(I mentored the Google Summer of Code project that brought the Android emulator's support for Hypervisor.framework to upstream QEMU).
Depending on the use case, you could still compile a custom version of Darwin, if you absolutely need to.
OpenCore Reference Manual https://github.com/acidanthera/OpenCorePkg/blob/master/Docs/...
OpenCore Vanilla Guide https://khronokernel.github.io/Opencore-Vanilla-Desktop-Guid...