This is usually because they have been put in a drawer or elsewhere and erased.
The annual gift card companies are somewhere around 80 - 90 billion dollars each year. It seems like think it be a cinch, with the many hundreds of products and services on the net or in nearby shops. https://Groups.Google.com/g/giftcard-mall-my-gift-info/c/lJb4jNQqwjY