Yes they resell the gift cards. If I quote the article: "... these accounts can all be cleaned out and deposited onto a gift card number that can be resold quickly online for 80 percent of its value"

Additionally, a quick google search for "sell gift cards online" reveals many sites that offer the ability to sell your gift cards. One example: https://www.cardcash.com/sell-gift-cards/

Quote:

Why go after hotel or airline rewards? Because these accounts can all be cleaned out and deposited onto a gift card number that can be resold quickly online for 80 percent of its value.

“These guys want that hard digital asset — the cash that is sitting there in your inbox,” Bill said. “You literally just pull cash out of peoples’ inboxes, and then you have all these secondary markets where you can sell this stuff.”

Some gift cards can be cashed out conditionally. For example, California requires that gift cards under $10 be redeemable for cash.

Outside of that, there's a huge grey market for "discounted" gift cards. That's probably where most of these are going.

Reselling for 80% of value per article.

they can sell a $50 gift card for $40 or something

I have tried to do this legitimately for unwanted gifts and its a lot of work. Posting a gift card on the normal buy and sell sites attracts every scammer in the country who all pretend to have sent payments or send fake paypal emails to you and get angry when you don't hand over the code.

And then even when they do pay you they could always tell paypal that the code didn't work.

There's sites you can sell them to, rather than individuals. I've sold lots to a few different sites and I've never had any issues.

Paxful.com