In general, merchandise costs are not based on materials or production costs. (They are to an extent, but not as much as you think.)
Retail costs are based on the manufacturer’s perception of “how much can I charge without losing sales”?.
So in this case, the store and the manufacturer have decided (probably because of competition) that they don’t have the ability to raise prices, because they will lose sales as a result. So the price stays low.
The beverage market is highly competitive. Arizona Tea is probably not making much profit per can. But they likely feel is is better to sell something and make a little money, than sell less because they charge too much.