Yet people aren't doing it? Why?
Because some junk science came out in the early 2000s (that has later been thoroughly discredited), and some celebrities picked up on it. And too many Americans would rather believe a celebrity than a scientist for some reason. That's it.
Some people drive drunk, drive without their seatbelts on, refuse to use a proper carseat for their kids, etc etc. It's all still against the law.