It's because young guys are still trying to impress people, and one way to do that is to buy a car as a status symbol. Old guys do it too sometimes if they never did it when they were younger. Most likely because they went to a preppy college straight out of high school and studied diligently. Trucks are useful for the college drop-out manual laborer type guys. But, like I said, they also want to impress people, so they care more about the style than the function.
Old guys with the camper shell usually have a solid career, and are more mature in that they know they have to devote their entire lives to their career in order to survive. And they are usually married or have given up, so they aren't trying to impress any ladies.
The guy at your job might have just been agreeing with you because you were at work. But, probably not because you're right, campers look lame. That's how America works. Anything practical looks lame to immature dudes. Anything ridiculous is SO SICK! It's a pretty simple observation to figure out.