Maybe it's a reasonable design decision. How often is the car going in reverse? Should you really be fiddling with the UI when the car is in reverse? Sure there could be a passenger, but is it such an inconvenience?
No, I agree that it's awful. I rarely want the volume when I get in and start the car to be the same as it was when I ended my last trip. And not "fiddling with the UI" is exactly why there should be a mechanical potentiometer knob that is always available by feel to let me quickly spin down the volume and get back to driving without being distracted or annoyed by the radio. The need for that in Reverse isn't any different than in Drive.
