This again? Really?
Apple doesn't lock down the GM of the annual x.0 release until the day before the iPhone announcement event, which means it is not being pre-installed on anything prior to then. Going by normal patterns, that means Apple would not be installing 13.0 on anything at any factory prior to September 10th. The phones don't leave the factory until 24-48 hours before launch day (probably Sept. 20), so they have plenty of time to install the GM. Normally.
But now that Apple has clearly stopped development of 13.0 and moved on to 13.1 more than 2 weeks before they would usually lock, that's a good indication that 13.0 is not happening at all. 13.1 is the new release candidate, likely because 13.0 was not going to be releasable, and something about 13.1 made them feel they could get where they needed to be sooner. Of course, here we are at Aug. 28th and haven't seen invite for the September event either. If we don't see one by Friday, it is pretty safe bet that everything is delayed, until 13.1 GM can be established.
We don't really know exactly what is going on, but I tell you confidently that the above bold is Not what is going on.