Due to impressive technology advances, cars could drive safer by themselves than if driven by a human being. It became harder and harder (at least for the well-developed countries) to get a car that you can actually drive yourself. Hacked cars was always a fear, though, so self-driving cars had extensive protective measures in place.
In the list of major damage/casualties during the Hacker Attacks, hacked cars would be near the bottom since less than 30% were hacked (and all hacked cars originated from certain companies--the other companies, if the world had survived the Ending better, could have used "Hacker-Safe!" in their advertising) and really didn't do much damage in comparison (it did clog quite a few roads up, though). However, the psychological effect of the hacked cars was far more destructive than most of the other Hacker Attacks.
Hacked military robots is scary, but if your own car can be used against you, that makes the attacks personal.