Yeah and the open source people gave up, it’s like giving you a free recipe for a beef Wellington in a world they control of food. Nothing uses Darwin besides Apple
And? The source is there. There is no requirement to do extra work to make it useful for anyone but yourself. They did not even need to release the source, but they did.
You made a claim about "proprietary forks of all the BSD stuff". The kernel is open source. The rest of the OS is written from scratch by Apple, and originally by NeXT, and is not a fork of anything.
Here's the kernel, including all the BSD stuff:
https://opensource.apple.com/source/xnu/xnu-7195.141.2/
You can compile it yourself and run macOS with your own kernel build. Here's a blog by Apple's head of XNU development explaining how that works:
https://kernelshaman.blogspot.com/2021/02/building-xnu-for-m...