Department stores don't offer you such choices, nor do automotive parts stores, restaurants, Best Buy or liquor stores. But, for some reason, grocery stores have deemed our decision-making skills essential to their profits and prosperity.
Some people argue that they have the two bags for different items.
You wouldn't want to put three gallons of milk in a paper bag because it would be difficult to carry. You don't want to put a loaf of bread in a plastic bag because it will be crushed up by carrying the bag. Then again, I don't see three gallons of milk fitting into a plastic bag nor do I see the bag sustaining that kind of weight. Bread is already in a bag, but we feel the need to put it into another. Enough about bags, though.