The quick answer is supply chain markup. Stuff isn't sold at cost because that's usually not a winning, sustainable strategy. Distributors (if there are any), manufacturers, and retailers will all want to cover their (varying) overheads as well as make a profit. The largest profit is generally made by the the retailer. A bricks and mortar store has markups of about 100%.

All the above is why you sometimes hear people talking about shorting their supply chains because it means lower trade prices, which in turn allows for increased profits, an increased ability to compete on price, or both.