People also know the risks of fucking with the radio, looking at maps, yelling at kids, driving while sleepy, or drinking and driving. Guess what?
All of those still happen in spades are for the most part of impossible to eradicate. With a combination of education, training (eg no passengers in the car for 3 months) and penalties, we can reduce them like the world has done for drunken driving, but people will continue to use their phones while they drive just like they've let other things distract them as long as cars have existed. The only real differentiator is that the phone lets us combine nearly everything into a handheld distraction as opposed to having 10 different proximate causes.