If U.S. cities had proper cycling infrastructure, I would expect many more adults would use bikes for local travel. But as it is, driving is certainly more reasonable for many people when the alternative is biking on a shoulderless road with deadly vehicles passing inches away from you.
Lucky for me, I live near the most bike friendly city in the country - and it's not on the left hand coast. ;)
If it was feasible and I lived within 10 miles of where I work, I would for sure bike. Right now, I commute almost 20 minutes in my car, so biking to and from work just isn't a great idea. If I lived and worked in the city, I would for sure bike every day. Even if I worked in the city, I would utilize the light rail for the majority of my commute. It sucks I would still have to drive 10-15 minutes to get to the light rail though.