Not sure why you are being downvoted, you present a valid point.

The trouble is that with mechanical parts it is usually very easy to see connections between elements - not so in digital world. I think the direction the car makers should take is to develop "microservices" with strict APIs, strict access lists and a guardian which double-checks if some requested operation really makes sense. That way if you root a media center you can't mess with the engine from there.

EDIT: I see from other comments that Tesla apparently does something similar. Too bad it's not standardized and open, but at least approach is right...