Mainly because fe is so far down on the list of priorities. Heck, $4 gas is BARELY able to get people out of sub-20mpg pickups and SUVs... and for many, fuel expenses aren't the biggest operating expense after the loan, insurance, repairs, and such are combined. We will probably have to wait for much higher fuel prices and/or a "worse" economy (in quotes because in spite of all the media hype and water cooler talk, a look around reveals quite a lot more people than ever before enjoying the trappings of wealth than the sufferings of hardship) and/or some sort of catastrophic event to see a widespread attitude shift that values fuel efficiency.
People are still in ego-driven mode, that is, logic isn't the dominant factor in their vehicle selection; what they think will impress the opposite sex or the people at church is still the biggest factor. Current mass psychology favors aggression over efficiency.
In talking to a guy that was curious of my Songi electric bike, I pointed to a nearby SUV and mentioned that to drive that thing downtown (less than a mile from where we were) and back would cost over a dollar... you could tell by the look on the guy's face that the notion of cents/mile cost had never entered his consciousness before in his life... and even when it did, he was rationalizing how to justify paying over a buck to go a distance easily and quickly walked...
For vehicles that make fuel efficiency a highly visible priority (Insight, Prius, VW L1) I think the tails could be longer but for sure there was an analysis of the pros and cons of such a move like parkability/garagability vs the incremental fe gain. The bias will change in favor of longer tails AFTER the consumer indicates they accept it and vote that it's worth it by buying such a design, or when there gets to be competition among manufacturers to have the slipperiest design, or something.
Some things are not done mainly because they don't really show up on the EPA mpg testing.
