Problem is we have become blase about automobile accidents. Cars keep getting safer and the death rate keeps falling, but cars are not safe, and an accident that involves personal injury can pretty much ruin your whole day, if not your entire life. Why do you think you are paying $100 a month for car insurance? So insurance agents can play golf? No, it's because of the massive payouts for medical expenses when people get hurt. (Well, at least I think it is. I couldn't find any data on how much insurance companies pay out. All Google delivered was useless consumer information tips, probably because I wasn't holding my mouth right.) Never mind the car, that is just a thing, and easily replaced.
While most people can manage more than one task at a time most of the time, the penalties for screwing up in a car can be catastrophic, and since rules have to apply to everyone equally, and since even the inept can qualify for driver's licenses, nobody gets to use a cell phone while driving.
Inspired by Dustbury.