I never thought that anyone other than the driver would want to connect their phone to the head unit in the car, regardless of how many other people might or might not also be in the car.
On further reflection, I think it's still overall not a good idea. If the driver wants to change the music being played, or the volume, or whatever, and there is a passenger in the car with them, then I would think it would be okay for the driver to have the passenger do that on their behalf. And that might affect the display.
But I guess I can wait to see if iOS 13 can change my mind.