I'm guessing it's more because "Ultra" versions, which "fuse" multiple chips take significant additional engineering work. So we might expect an ultra M4 next year, possibly after non-ultra M5s are released.
They released the M2 Ultra
Good point, I forgot about that. Maybe it just got really delayed in production.
Reportedly Apple is using its own silicon in data centers to run “Apple Intelligence” and other things like machine translation in safari. I suspect that the initial supply was sent to Apple’s datacenters.