It's the greed. Apple only makes around 8% of revenue through hardware sales of all Macs combined. "Services" (App Store, iCloud, Music, TV+, ect.) make more than 3x more revenue. Then, profit margin on services is again 3x higher than on Mac hardware. So they really want all Mac users also use Services.

If your proposed change increases Mac sales by 1%, but only 0.1% of users install Asahi, they lose money.

I'm still watching out for Asahi progress, amazing project. USB-C displays and the M3 will come (and I don't care to much for the rest), that makes a refurbished macbook air an attractive proposition.