That is the argument I often have with my American wife - my usual counterargument is that in suburban areas it is indeed difficult to develop a viable transit system due to low population density and large distances involved - but that is altogether different from the reason why many people choose to live in such areas and use cars as their only means of transportation. In fact many people stubbornly insist on driving in areas where driving is hell due to traffic congestion and there is a well developed transit system (e.g. Washington, DC).
It is my experience that many US-ers are afraid of anything unfamiliar to them, especially people who look differently than themselves. There are many reasons for that. Because they are afraid and fearful, they escape from interaction with other people. Isolated suburban dwellings and cars make that escape easy, while menacing-looking SUVs also double as a hedgehog defense - "I look scary, back off."
I have been to many places around the globe, and the US-ers definitely looks like one of the most alienated folks, afraid of many things, and awkward in most social interactions that go beyond conventional and rigid small talk. They are also among the ones most obsessed with their own security and going to unusual, but most other people's standards to obtain it.
Now connect the dots.
In sum, I think that wile there are undoubtedly structural reasons why people do not want to take the bus, most of it is caused by personal sense of insecurity, fear of interaction, and a desire to escape and isolate oneself from others.
Wojtek