If the rightful owner (the holder of the giftcard) wants the money, then they can go to the store and use the gift card. Pretty simple.
And if they don't the store should keep the money. That's theft, of which you apparently approve. Unfortunately, this is a nation of laws. Get used to it or move to Zimbabwe.
No, its not theft, because when the someone bought the cardholder, it was understood contractually that the store would hold the money until the user sees fit to claim it. If they didn't feel like claiming it, that's not the store's nor the state's problem. The state has absolutely no business taking the money in the mean time.
Here's the other kicker: this can cause some severe problems with interstate commerce. Lets say I have a relative in Maine, and they get me a gift card from say, Burger King, and send it to me in Nevada. I let it sit in a sock drawer for 2.4 years until I remember its there and go use it.
The store, since there is no expiration date, HAS to redeem it for its full value. However, in order for them to get the 60% of the funds back, they now have to find out where the card came from, and apply for reimbursement. This is direct interference into interstate commerce, and puts undue burden on the store owner to get reimbursement.