Cyclists differ from other workers not only because of their small numbers, but also because they are much more likely to enjoy commuting to work.
According to this report, 59% of cyclists enjoy their commute, compared to 37% of those who drive a car to work. Furthermore, 19% of cycling commuters report that commuting is their favorite activity of the day, compared to only 2% of drivers.
My theory: they'd rather drive but can't because of finances or too many DUIs. In my area (and probably yours) most utility cyclists are recent immigrants who see bicycles as a symbol of poverty that they're trying to leave behind. They came to the U.S. to take part in the American Dream, and part of the American Dream is a home in the burbs and a big fat SUV.