Companies actually make a lot of money on gift cards in several ways. One, they get the money right up front. Inflation generally lessens the dollar's value over time. Now, that's not a big deal for a card over a few months, but we're talking billions of dollars one the whole. It adds up surprisingly fast. Your money now is worth more than your money in a couple of months.
Another huge pot is lost or never used cards. Again, this is a small percentage overall, but it adds up over the millions of cards out there. Some cards just get tossed when they have what the owner deems is a small amount left--a few cents or even a few dollars.
It all adds up.