There have been times when I've left a bag behind in a grocery store, and I'm sure that many other people have done that as well from time to time. I think that when this happens, the blame can be placed on both the customer and the cashier or bagger, because sometimes when a cashier is bagging your groceries, the bags will be behind the counter and the customer can't see if they were handed all of their bags.
Also, it's the customer's responsibility to ask the cashier or bagger to check and see if they gave them all of their bags before they walk out of the store.
