Only two posters have mentioned the status issue, but I'll give it another go-round. Of all our many status symbols here in the US (and we work with a lot), cars are one of the very biggest and most universal; this is true across nearly all US social groups, in terms of class, race, ethnicity, etc.
The use of cars as status symbols is often important at work, too, whether it's for impressing co-workers, clients, or just yourself while on your commute.
Sure, many people here in bikeforums are predisposed to already think highly of riding bikes for transportation or utility, but we're a small minority in the larger USA that respect. And even among this crowd, there are probably many who mostly think of cycling in terms of fitness, (competitive) recreation, and so on, but not for basic transportation or utility. That perception of cycling is simply not a strong, positive association in our culture.
(Also, these issues extend to the use [or not] of public transportation in many cities, as well as cycling.)