Most low to mid level hoarders I know come from a background of some form of scarcity. They usually grew up poor or were there during war or something like the great depression. Their paranoia that they need to cling to every item they come to own because they might need it and never be able to obtain(afford) it again is less crazy in that light. Less commonly I see people with unusually strong attachments to memories an item invokes, or a desire to treat an inherited item with religious reverence to honor the deceased. Upper-middle and above class people who were always able to buy whatever they needed/wanted rarely seem afflicted by hoarding.