One word, Daimler. They controled Chrysler at that time and even though the Charger show car was a hit with the public, they were too concervative in their views and didn't understand th American car buyer. So they produced a plain vanilla version of the car. Today we have in the new '11 Charger, without Daimler's interference, a car much closer to the original show car.
If this isn't enough to convince you, think back to the PT Cruiser, written up by the press as the most inovative car of the last 40 years, the beginnings of modern retro design. Think about of the color choises. Gramdpa and Grandma would be right at home with Daimler's dark and drab, bland choises. It took (American) public pressure to get some of the hotter colors.