How much do credit card companies make on unused gift cards?

Is there a way to see how much the credit card companies collect yearly on unused gift cards?

I am referring to the gift cards that are administered by the credit card companies (i.e. American Express gift cards, or Visa gift cards).

I always make it a point to use up literally every penny, but I’m sure there are tons of people who have change left on it at expiration and a ton of people who forget about them completely when they expire.