And those are really the core use cases for AirPods, HomePods, and CarPlay, the contexts where a hands-free eyes-free interface is most useful.
It would be nice if it could control 3rd party apps too, like GMail, but being able to control the stuff that Apple themselves have built doesn't seem a lot to ask.
However, the original Siri, obtained from SRI ("Siri" = SRI) was pre-LLMs, and there should have been no more concern over accessing system settings or controlling apps than things like reading/sending messages. For some reason Apply completely dropped the ball with Siri; initially it was expected that they would expand it into revenue generating areas like restaurant reservations etc, but then nothing. I'm not sure what documentation exists, but even today it's not clear what Siri is actually capable of.