IPHONE Music Auto Play

Why does Music start to play from my IPhone when I get into a vehicle with “Auto-Play”? There is seemingly no way to turn this off without disabling Bluetooth. The only way I have found to stop this is to turn my car to radio. Swiping to close the Music App doesn’t stop it either.. Beyond annoying.. it just seems Ike the car entertainment should control what devices play through it and not the other way around. This seems like such an easy fix there must be more to it..