I think it's quite simple- in the U.S. a consistent demand for efficient cars isn't there. Motorists may complain around the water cooler or for news sound bites when gas prices go up, but for the most part that's as far as the action on the consumers' part goes and they continue to rack up the miles in the biggest thing they can get their hands on.
Most don't use rational criteria for choosing vehicles; it's more about status and perceived image than anything. If there was any rationality in vehicle choosing I wouldn't see 75%+ of the local traffic mix using 5000 lb V8 4x4s for transporting what is usually a solo 200lb (or maybe 300 lb) occupant.
Another factor may be that most people really only have a vague notion of what their true expenditures are, thus the outrageous and totally disproportionate costs for personal transportation are never really given any consideration, other than can the car payments and credit card gas purchase payments be made at the end of the month?
During an economic downturn or energy price rise there is a short-lived clamoring for economical vehicles, but as soon as the majority feel like they have two nickels to rub together again they bail out on the "austerity" of not being flagrantly wasteful. I guess it is a treat to be wasteful?
There is a market segment that makes efficiency and economy a priority, but it's quite small compared to the "norm". The niches are tougher for manufacturers to make a business case to cater to; to sweeten that pot the profit/unit has to be proportionally higher just to be average... OR sometimes the mfgs are compelled to make such vehicles to meet government mandate (I think the Metro falls into that category; GM needed to meet CAFE).
Past successes like the Model T, classic Mini, and the classic VW Bug don't fit neatly into my paradigm; they're economical and cheap yet achieved cult status anyway. Maybe they succeeded because they were just too much an awesome blend of style and value to be overlooked. Or maybe the times were different then and we are further along into the Idiocracy cycle now...
