Why dont cars with bad mileage such as a hummer, have to put mileage on the sticker?

Supposedly all the car companies want to go green and be environmentally friendly, yet the gas guzzlers such as the hummer dont have to put how bad of mileage they get on the sticker, why is this?|||Because, it has many other positive points. People don't buy it for better mileage.|||because the federal government requires the manufacturers to do so|||Vehicles, especially trucks (which the Hummer is considered to be), over a certain gross vehicle weight are exempted from having to list fuel economy.