macOS sandboxing is deliberately limited just enough to prevent anyone from truly implement Darwin-on-Darwin containers. People have been discussing about this for a while, see https://github.com/apple/container/discussions/611

In general I understand the rationale behind Apple's decision. They sell hardware, and there's real demand for macOS on servers to run build jobs and other Mac-only tools. Giving you the ability to run multiple containers on a single Mac would end up turning a 10 Mac Mini order into a 2 Mac Minis order for most people. Rest assured, even if it would be technically possible they'd find a way to cap it somehow via the EULA or whatever