Body in white Challenger?

Even as a drag racer, I never understood the modern body in white programs, be in gm, ford, Chrysler. Opposed to a shell that was missing half the body panels, a running driving 6 cyl challenger, or even a 5.7 car that was tapped on the nose, could be had for the same, or less $....and you'd have a title ta boot.....and glass....and seats....and carpet, yada yada