In many parts of the US it’s typical to start driving several years earlier than that, and realistically there is no way to get anywhere other than by car. Until kids can drive, they might quite literally be unable to go anywhere or do anything without an adult to drive them. It’s sprawl to an absurd degree.

Even where bikes could theoretically be used from a distance perspective, it would likely be way more dangerous and way less practical (no bike lanes and every road is full of cars, no bike parking, you’re never getting to a bike shop for repairs without a car, …)