Apple's whole thing is hardware + software working together. Endless other options available to Linux users. They'd also need to be prepared for people bringing laptops to stores with hardware problems that aren't running macOS. Again, more burden for Apple for no gain other than winning over a couple of dozen users.
Do you seriously think someone who installed Asahi is gonna walk into a genius bar and ask for help with it? And often enough that it becomes a burden??
And according to their stats page that sibling linked it’s more like a few tens of thousands of users.