If I can't remove the SIM, I can "Close" the account. If they won't let me close the account I can go to my bank and have all payment for the service stopped (worst case - I can get a new credit card or account to stop the direct debit). Why would I want to pay an additional monthly fee for the car.
I don't think the car manufacturer is going to pay a fee for every one of their cars manufactured especially as they have no way of knowing when the car is no longer "on the road" and will have to pay for the service "forever".
I can see a booming "After Market" switching the component with the SIM between different cars to give false information.