And how would you activate CarPlay? At the moment it's wired-only, and I'm skeptical as to whether it could be made to work over Bluetooth in existing cars. If you bought a new car today with wired CarPlay, you might still be driving it in 5 or even 10 years, and you really wouldn't want to lose the ability to actually use CarPlay in just a year or two.
That being said, how would you service a portless phone? There would be no more DFU mode.