4,100Lbs is the current average weight (and 2004 was already at 4K so I’m not sure if this statistic counts SUVs/trucks or not)
CAFE standards required proportionally greater economy improvements in compact cars than in medium and large vehicles. Rather than attempt to meet those standards, manufacturers just stopped producing their smallest cars.
Fuel economy has worsened, because the average car on the road is bigger and heavier now than 30 years ago.