Apple spent significant engineering effort modifying their iOS bootloader to support third-party OSs—then neglected to tell anyone how to actually make a third-party OS. Whoops! Have fun!
And to be clear, this is absolutely preferable to Apple selling fully locked-down Macs. And, I realize that macOS will always be Apple's first priority, and that writing documentation takes effort.
But would it really kill Apple to connect Marcan to an engineer, who could allocate 30 minutes a week to answering questions? Is there some sort of legal liability involved? Security concerns? Brand safety?
The Asahi team is comprised of people who clearly enjoy reverse-engineering, and if everyone is having fun (and creating an awesome Linux port in the process), perhaps that's all that matters. But I still find Apple's choices confusing.