It probably makes sense for places that sell anything in glass containers (especially alcohol), because all it takes is one dumbass dropping something on the floor and someone else walking through it barefoot to have a liability lawsuit on your hands. Whereas if you put up a sign forbidding that and someone manages to sneak in anyways, you can say it was their fault for violating store policy in the first place.
"We were trying to give away cases of the food on Wednesday, but people were turning it down because they had no place to store a case of tomatoes, or cauliflower."
Duke Nukem is the name of the protagonist you dingus