I just don’t think there are a bunch of Apple people sitting around a cafeteria table at Caffe Macs ruminating about when the next beta should drop and whether an extra beta release would be useful. I suspect that the beta release schedule (really, the entire iOS 17 release schedule) was etched in stone no later than late last summer and possibly even earlier than that. Again, absent something as drastic as the EU regulations, they are not going to change a thing over the entire lifecycle of a major iOS release.
Everything has to go lockstep and be tightly controlled to ensure that the new iOS release (here iOS 18) is ready in time for the launch of the new iPhone in September. Because that’s where the
is.
I spent 20+ years working in a large manufacturing company (think very
very large). Product release schedules in a large engineering /manufacturing environment are about as sacrosanct as something secular can be. Missing design and release milestones is career endangering. No one is ad libbing.