Car manufacturers only make cars people are willing to buy. As long as the cost of petrol is a fraction of the total running costs of a new car nobody is going to care unless money is not an issue or the environment (ecology=long term economy) is more important on a personal level.
More like they only make cars the bean counters think people are willing to buy.
Just look at the Pontiac Aztek!!
It has been a slow progression, but look at a lot of high mpg cars today. Now look at the home made boat tails that some of us have done in years past. Grill blocks, lowering suspension to improve aero, ect. The auto manufactures are coming around.