For good reason. In 1978, the congress critters passed the gas guzzlers tax:
The typical land yacht, with about 15mpg, pays about $4,000 in gas guzzlers tax.
The idea was to discourage big ugly oversized non-commercial vehicles. However, they exempted anything over 6000 lbs GVW. So, in accordance to the law of unintended consequences, the industry simply delivered monstrous vehicles that officially weighted 6001 lbs and save a bundle on the taxes.
Of course, the government derives substantial revenue from taxing what are now economy and mid size cars, so don't expect the situation to change in the foreseeable future.