Because your phone is designed to do that, a car is not. Besides, iirc the most car services don't even use the car hardware itself to enable their service. The

Because your phone is designed to do that, a car is not. Besides, iirc the most car services don't even use the car hardware itself to enable their service. They usually install secondary systems for communication with their servers somewhere inside the car and then communicate with the cars controllers. So its not even a matter of how expensive the car is, its a matter of how well designed the rental companies hardware is.