Fact is, modern vehicles have to meet strict, federally mandated crash protection standards and must do so for the expected service life of the vehicle. Since rust destroys the strength of metal, it must be prevented. Manufacturers spend more money on the metal finishing aspects of vehicle construction than anything else. Afterwards, the vehicle is coated with a thin layer of its final color, so thin that it takes only about a quart of paint to cover a full-sized car or sport utility vehicle. On top of that are sprayed several layers of clear paint, leaving the deep luster we have come to expect.
Color costs money.
The tinting materials needed to create those beautiful shades are very expensive to create. Therefore, some years ago manufacturers asked the paint companies to come up with more cost-effective processes. Less color is used and clear enamel is cheap, so everyone is happy - almost. It's still terribly expensive to paint vehicles. Paints contain toxic solvents and other organic compounds that pollute the atmosphere and cause illness.