The tech community exploded last week when Apple released beta 1 of 13.1, before 13.0 was even confirmed GM or hit devices publicly.
There was a lot of speculation and funny bits, people thinking that Apple only develops one piece of software at a time [ha], others saying that 13.0 is somehow so buggy that it's going to be updated right away to 13.1, and the public will never see 13.0, and even more speculation and chaos when a fake document went around trying to spell out the plan.
I think the most obvious thing Apple is doing here is trying to steer clear of what they've done in the past. In past years, iOS beta usually reaches a point during the summer where it needs to work on new hardware. That means prepping it internally for release to devices that are flashed at the factory. In order to support hardware, it's going to have information about that hardware, like, dual-sim support, Face ID, or the brand new iPhone X entirely with its new features and contemporaries in the product line.
So, if you're Apple, what do you do when the late betas are leaking hardware? Or, when employees who have access to the latest seeds hack on top of their boot arguments to get them to display features they aren't supposed to have access to?
You keep the late/final seeds close to heart. So, instead of releasing iOS beta 9, like everyone was expecting, internally and externally, you release the next major release, 13.1. This won't have any of the features that are hidden and exclusive to the near gold master of iOS 13, which is needed on the devices that are shipping next week. But it will have new features that were pushed from the 13.0 release in September, which will allow for more testing, and keep the developer community happy.
Anyways, this whole post is just me speculating off of what little knowledge I have of internal processes. And to be here when 13.0 is actually be released and say "I told you so" to all those people that think that Apple's somehow:
1: Skipping a public release of 13.0
2: Shipping iPhones with 13.1¿¿¿ and not having a great upgrade path
3: Is burning down Apple Park and erupting into chaos because they happened to seed the next Beta before a public release
It would help if Apple Developer Relations, I don't know, had a public post about this? Pushed to say "Maybe don't just auto update people on the latest beta to 13.1?"? Communicated whatsoever? Related to the developers?
Although, I think Apple should've realized that there is a certain developer/user hostile feel to releasing a point update on the same seed as the previous major update, which confuses users who may be public beta testers who may want to revert back to shipping software before November.