There is evidence that, for American young people, possessing a drivers license is less of a priority than it was 30 years ago. According to The Daily Beast, only 61% of American 18 year olds held drivers licenses in 2010, a decline nearly 20 percentage points since 1983, a year in which 80% of 18 year olds were licensed to drive.
Evidently car ownership is less common among younger adults. Why the drop-off? It appears that cost and necessity are at the core of the phenomenon. The article cites the recent increases in urban mass transit services as a viable substitute for driving a car.
In short, it seems that for some younger Americans, driving is not an absolute necessity, and it saves money for some not to do it.
The Daily Beast: Young Americans Show Reluctance About Becoming Drivers
"The simple answer to the question of why the drop-off is that many young people just don’t need a car."
---------William O'Connor, The Daily Beast