Probably because people don't collect them until they need them and the poor person doing the order ends up storing a garage full of jars for the convenience of others .... and if payment is not collected in advance of the order .... good luck getting the money out of some people.... and woe betide if there is a dented lid in the box or a broken jar.
Been there and done that ....unless, like a few associations, they have a storage facility and a proper shop ... anything left to the generosity of a member is a risk ...