Apple developers are a captive audience, they will pay their annual hundred bucks and develop for iShiny no matter how crappy the docs are. There are just too many rich users and clueless PHBs demanding apple development to miss out. If those reasons went missing and Apple really had to compete for developer mindshare, docs would improve.
Which leads to the solution: Quote a lot more for Apple development or don't develop for Apple, and as soon as the stream of app updates and releases dries up, Apple might react. But not before.
iOS is Apple's bread and butter, and they make good money off those developers. It's in their cynical self-interest to spend the money to have the best documentation in the game, and it would even pay off inside Apple, with better APIs and better resources for their in-house teams to develop against.
It seems like a genuine institutional dysfunction. Apple has a culture of secrecy (which is necessary) and a result of this is deep siloing of teams. How this leads to documentation being such an afterthought is murky, but I suspect that's the cause, rather than merely being complacent about their walled garden.
I can also do handwaving culture arguments like apple design in a minimalist fashion, so everything that can be left out will be, including documentation. But I don't like those, I hate to diagnose cultures I only read about.
However, apple is a business, and leaving out docs makes business sense and is an easy and straightforward explanation.
It's a puzzling omission, given that building App Store revenue is such a priority, and they feed the supply side in a number of other ways. I don't think they're doing it on purpose, they're just bad at it.
Which leads to the solution: Quote a lot more for Apple development or don't develop for Apple, and as soon as the stream of app updates and releases dries up, Apple might react. But not before.