Well...here is the thing....people have a herd mentality. they hear something good and don't want to be left out. especially when others they hear about are making money. doesn't matter what. they want in.
It sit on the shelf or counter and generates rev. There is no work involved for the store owner to do anything. sells itself. why wouldn't anyone want it? especially hearing and knowing a half block away Joe shmos shop is making bank on it.