As a screen reader user, Apple does have a first party screen reader, VoiceOver, and does indeed not let you run a third party one. In fact, it does not work well even on the more open MacOS. So essentially it's VoiceOver or nothing. Luckily, especially on iOS, VoiceOver mostly works well.
I'm glad it works decently on iOS, at least. my mom has little central vision, and she struggles on iOS just using high contrast plus scaling plus magnifier. I think she has just enough vision to not absolutely need VoiceOver but it still makes using her phone a frustrating and tiring experience.
I don't think they're "trusting Google" with anything. It's a Google model run by Apple, just like you download a model from Hugging Face to run when you want to.
In this case I think it is true that 3rd parties can not be trusted with this capability, but Apple brought this on themselves by creating a ton of other capabilities like AirDrop, Airpods integrations, and apple watch capabilities which would have been safe for 3rd parties to use but keeping them locked down so you'd get a better experience with Apple accessories.
- Apple has powerful capabilities in iOS to enable Siri AI.
- EU's DMA requires them to allow users to install third-party AI backends.
- Apple doesn't think parties other than themselves should be trusted with those iOS permissions.
I guess it'd be like if Apple allowed a first-party screen reader for iOS, so they refused to allow third-party screen readers.