Lou Trottier says the first reason relates to the warranty and the second relates to the challenge in painting the repaired ...
Contractors swear by these rust-removal tricks for saving old tools.
While fixing surface rust is usually easy to DIY, structural rust damage to the frame is an entirely different story and requires a special approach.
Truck beds have a difficult life. They live out in the elements, they have things dropped and thrown on them, and generally get beaten up while being the reliable, utilitarian vehicles that they are.