Gift cards don't always get redeemed, and of those that do get redeemed, many are not redeemed right away.

It varies by issuer retailer and market category, but generally (rough estimates) about a quarter of cards remain unredeemed after one year.

That unredeemed amount is (eventually) booked as "breakage", which is pure profit to the retailer.

So they are getting cash for the sale of the gift card, and booking that as a liability until it is redeemed. So a gift card is like an interest-free loan (albeit with uncertain repayment date) to the retailer.

Why would they give that up? I suppose they could operate an underfunded mint and add funds as needed based on card redemption, but I suspect an electronically transferrable card balance would increase redemption rates. (e.g., due to regifting, as one example. I got a Best Buy card, but I'ld rather have the sats so I trade it online -- and since there's essentially no risk to the buyer I can sell it near its face value).