>>13Some automated systems like anti-lock brakes or stability/traction control need calculations to know when to activate and to what extent. Also, cars have lots of sensors that let you know when something's about to go wrong, like a door being open, your next oil change getting closer or a system running in non-optimal conditions.
That doesn't explain the bloat, though. As complex as a car might be, having an executable size of more than 10MB just to read some pin inputs is way beyond retarded.