What no one seems to be thinking about is that a fifth wheel hitch in the bed of a pickup is useless unless the mounting plates on the frame beneath the pickup bed are taken also. You cannot just bolt a hitch to the bed of a pickup, it would rip out or rip the bed off the truck. Have you ever looked underneath a truck to see the typical six small bolts that hold the bed on?
About the only use I can think of, would be for someone who had some serious wear problems, and want to steal some parts. Even then, have you ever heard of anyone doing that?