“There is a cost to business for issuing gift cards.”
Yes but the cost is lower than the amount of free interest received on the dollar amount of the card until it is redeemed. And less than the amount that never gets redeemed.
If they are such a poor investment why do companies offer them? For the same reason they offer mail-in rebates. They know many of them will never be returned and therefor it’s free money, or you might say theft.
Businesses should be no more responsible for the unused gift card than for the uneaten fruitcake or the unworn necktie. They sell the cards in good faith, prepared to honor all of them but knowing - as a practical matter - that some will never be used and others only partially used.