Another thing is that cars now are so bloated and heavy that is not helping the mpg too much.
Thats what I was going to say. Cars from the early 90s are lighter because not all of them had all the safety features like front/rear/side/top/bottom airbags, or other luxuries like navigation systems, in dash cd players, seat belts, heavier beams in the door, overall a larger frame altogether, etc.
It's not that it's getting worse gas mileage persay, it's just heavier. A 2000 Civic coupe is 2612 lbs without a driver, a 1990 Civic coupe is what 2100 +/- lbs without a driver?