What is the core argument why a gift card would ever be used instead of cash?
I can see if someone didn’t have any money and had a card and wanted to try and sell or exchange it, otherwise? Cash might have some limitations but none that are worse than a gift card.
Cash requires in-person exchange. To use it electronically, you’d need to participate in the formal banking sector. Many people can’t or don’t.
Instead you can take your cash to any of a large number of retailers and acquire a card that sits outside the tight credit/debit-card regulations. That card, thanks to the wide reach of various multinational corporations, has broad (and cross-border) value and is suitable for electronic exchange. All that in exchange for a small(ish) tax (the price of the card plus whatever discount the recipient/exchange applies to its face value), and less recourse if you’re scammed or you screw up somehow.
Incidentally you might be interested in @patio’s description [0] of Japanese konbini (convenience store) payments. There, your remote payee gives you a transaction number. You take that number to your local convenience store and hand them the cash to complete the otherwise-electronic transaction.
[0] https://www.bitsaboutmoney.com/archive/payments-in-japan/#:~...