Part of the problem is that it would be a significant amount of work to create and continue to support and maintain it, and all it would get you is the ability

Part of the problem is that it would be a significant amount of work to create and continue to support and maintain it, and all it would get you is the ability to run Mac OS applications inside of a container, and there aren't a huge number of users who want to do that. Most likely people would want to run Linux in their Docker containers, and that requires some form of virtualization.