The problem is that AI development is a completely different beast to regular software development. The iPhone was based on a mature existing OS (OS X), and although I’m sure they were keen to get it to market, they weren’t under any particular time pressure. The UI may have been a bit fragile at the WWDC demo, but they could be confident a few late nights and weekends would sort it before release. The original iPhone was also very much a v1.0 release, aimed at early adopters. But that was OK, as there was already enough there to get everyone interested.
The AI demo is September 2024 was more like the Mac Pro pre-announcement in April 2017, after Apple suddenly accepted they needed to build the 7,1. They acted like it was already well into development and customers just needed to hold on for its release, when in reality they’d just started work and it would take years. Unfortunately, in this case the iPhone is their flagship product, and AI is burning hot right now (granted, much is hype, but still).