It's not a problem for banks. They don't seem to feel any need to put an expiration date on their depositors' money.

Any sensible company should account for the gift card balances as a liability on their balance sheet exactly the same way a bank does its depositors' money.

The potential problem is that predicting how much liquidity you'll need to fulfill those liabilities in a given year isn't so easy. Banks are regulated to ensure that depositors are never out of their money. Some businesses have gone under as a result of getting this wrong with gift cards.