Based on the virtualization framework documentation, this seems very intentional. My guess is that they do this because their development processes only assure

Based on the virtualization framework documentation, this seems very intentional. My guess is that they do this because their development processes only assure that the macOS version shipped with the hardware works on that hardware. And the virtualization layer is really thin. They see no reason to spend the extra QA time, but rather have everyone upgrade to the latest macOS version their hw support.