If Moana had come out, we would not have Sams, we would not have X1000, we would have nothing new because there would be no market. We would all be tied to using Mac cast-offs.
Many of us don't want that. By releasing AOS 4 for Macs we would be tied down to second hand Macs for the lifetime of AOS 4, I'd much rather have spanking new hardware even if it is new hardware.
If you want to use old Macs, use MOS. If you don't, use AOS. Be happy with what you choose, and let other people be happy with what they choose.