Why do people give their scrap away?

I've noticed sometimes that it is their way of paying for your gas/time to come and haul their stuff away. Since most people who just give away scrap and valuable materials, it is because they just don't want to fool with the trips to the yard/dump. They call you in to haul it off, and don't ask for anything in return because they really don't know how much you'd get for it. That is pretty much what someone told me when I picked up from them just the other day. They said they had thought about taking it in themselves, but the yard was further away than comfort, and they just didn't have the time.