What ends up happening, I think, is this idea of one-upmanship which is based on status. You see someone with a fancy truck, and you think, "I want to have a cool truck like him!" - and so you spend money at the chrome shop. But no matter how much you spend, there will always be someone who spent more. You start down this rabbit-hole, you never know where it will take you.
Decorating trucks, however, is not limited to the United States.
When I was in Japan, they had similar trucks, and they even had their own television show, sort of like "BJ & The Bear" in the 1970s. These truck drivers with crazy-decorated trucks would drive around and solve mysteries, and then come to the rescue, lights a-flashing.