* Apps are already logged in, so no extra friction to grant access.
* Apps mostly use Apple-developed UI frameworks, so Apple could turn them into AI-readable representations, instead of raw pixels. In the same way a browser can give the AI the accessibility DOM, Apple could give AIs an easier representation to read and manipulate.
* iPhones already have specialized hardware for AI acceleration.
I want to be able to tell my phone to a) summarize my finances across all the apps I have b) give me a list of new articles of a certain topic from my magazine/news apps c) combine internet search with on-device files to generate personal reports.
All this is possible, but Apple doesn't care to do this. The path not taken is invisible, and no one will criticize them for squandering this opportunity. That's a more subtle drawback with only having two phone operating systems.