"Cars are a very inefficient transportation technology for too many reasons to count. They take up huge amounts of space but get driven around mostly empty — the average private car in the U.S. carries only 1.6 people. A lot of the time, people drive distances that are short enough to easily walk or bike — 28 percent of car trips are a mile or less, according to the Governors Highway Safety Association."
I guess it's more about freedom of movement. And in many cases owning a car is almost mandatory in North America. Sure, I don't want to spend that extra money on car and tires and services if I could.
I’m skeptical of that mile or less comment. Most likely it involves picking up groceries or other heavy goods, transporting children, and ignores inclement weather — all which are difficult to impossible by bike and a large hardship by foot. The US is largely not built like Manhattan or European cities.
One other note is the climate in the US is hotter and more humid, which makes perspiration from simply walking a mile a much more impactful exercise than in say London.