“Siri” (whatever it has morphed into) is a pervasive DWIM engine in iOS these days. When you do a search for an app Siri decides what to display (e.g. when I go to a certain location with a “smart” lock and pull down search, the app for that lock is always offered first, but never in other locations).
These days the voice part is just a UI mode. I use it on my watch and occasionally on my phone when I am wearing earbuds and my phone is in my pocket, but have it disabled on my Mac.
I'd be happy to have a voice assistant that was actually smart. Every few months I ask Siri if it's powered by a language model yet. So far it hasn't even been able to understand the question.
I'm also in the situation where I use Siri for nothing, but I want to use CarPlay. I don't use the voice control for anything, in the car or otherwise. How does it make sense to force me to have Siri enabled?
There's a bunch of parts of CarPlay which assume you can use Siri. Interacting with notifications, sending / responding-to messages, searching for things in maps, etc. Apple could disable everything that would kick itself out to a Siri-interaction for input, but that'd probably feel confusingly-broken.
