It's the flavor of the week, in most cases. I agree whole-heartedly. It seems more like someone made a suggestion, and has been widely ignored.
Here's a clue:
If you can't get AT LEAST the EPA rating for your vehicle, YOUR fuel costs $3.00/gallon.
Those of us who learn, adapt, get better fuel efficiency, get a break. We only pay $2.00/gallon.
Exponentially, the discount could multiply, representing various levels of efficiency and the rewards associated with them. If you get 30% better than your EPA rating, you get another 10% off fuel prices... hence, $1.80/gallon. 50% better than EPA, 25% less - $1.50/gallon. More than 75% over the EPA rating - $1.00/gallon.
If you can't pay $1.00/gallon for fuel, drive less.
Conversely, the less you get under the EPA estimate, the more you should have to pay... like a fuel tax system.
I think people would quickly learn to get better gas mileage, for sure.