Now that, perhaps, political and social momentum may perhaps be slowly moving towards doing something serious about the problem thirty years too late, here goes:
There is a general human tendency to view oneself as the standard model for one's own society and/or all humankind. Conservatives and the socially privileged are especially prone to this, so that any suggestion that "we" are doing X the wrong way is interpreted as a personal attack that must be defended against.
A closely related truth is that we Americans are raised to believe that a big car and a big house in the suburbs are things that the proverbial boy raised by wolves is supposed to instinctively want. We have been taught to see the attainment of these things as proof of being good; of being responsible, productive, loving and protective of one's family, etc. Now we have the specter of man-made climate change to suggest that this conventional dream is not only not innately virtuous but downright harmful. Many people who have spent their lives striving for and then prided themselves on attaining this dream cannot tolerate the thought of having been fools who prided themselves on a lie. They cannot stomach the implied charge that by having simply 'played by the rules' they have brought harm upon their fellow humans. They would rather believe global warming is a Trojan horse, cooked up by the losers to change the rules of the game by foul means.
I would add a couple minor points from what I've personally observed. There is a friend of mine, White as I am, who was once called nigger by as passing car while biking down a Kansas street. As far as either of us could tell he was called a nigger strictly because he was riding a bike. In many parts of this country there's a lingering sense that there is no such thing as willingly choosing to walk or bike any distance in any weather. (And certainly not to ride public transit with Those People) Not taking your car to wherever you're going is in itself proof of indigence, or even of being a dangerous fiend out to prey upon the children. My friend does have a car, as do I. I use mine almost exclusively for medium or medium-long trips out of town, otherwise I walk. I've heard cat calls of 'get a car' or some ruder equivalent more times than I can count.
I have also seen within some of my family an absolute, literal, 1-to-1 equation between the automobile and masculinity that is believed with utmost sincerity. Whether they think the millions upon millions of humanoid males who lived before the car was invented spent their lives with a constant sense of missing something I don't know. Or maybe they believe in some natural evolution between the horse and the car and that every true American man is a shining knight. Again I don't know.