When people are moving they want sturdy, well made moving boxes . Most storage facilities do sell an extensive storage and moving supplies. It is convienient for the mover who has just rented a storage unit to get boxes and supplies at the store, its killing two birds with one stone per say. Movers want everything to be easy and logical so if they come in to fill out their paperwork or come in to drop things off in their units they could get all the supplies that they need right there.