On the other end of the scale we have Tesla, which clearly does very little testing of their media systems, and pushes updates over the air, so things get broken or changed with every update. But "hey, it's not a big deal, we'll just push another update in a month!" - that's absolutely not acceptable with cars.
For example: https://medium.com/@michaelmeier_90534/tesla-model-s-is-grea...
I would be absolutely furious if my car did this. I would rather have a shitty system that stays shitty for the lifetime of the car, than have a good system that gets broken through an over-the-air update.
I mean, if an attacker has physical access to the insides of your car, all bets are off and is now his vehicle.
Remember it's not just the internet that makes you susceptible, it's any network.
I mean, I take your general point, but I'm almost certain that 99.9% of people breaking into cars do it to steal them, not to install a virus that will track your location or make your car crash. Both of those can be achieved trivially without even opening the car.