Because the stock value doesn't reflect real (book value). By and large, stock value has nothing to do with how much a company can really cost on the market. The value of a company in the stock market reflects the WINDOWS of traders about how much a company's shares may cost in the future. I mean, quotes reflect stockholders' expectations as to whether a company's shares will grow in the future. If current stockholders believe that stocks have peaked, they will start selling them and quotes will begin to fall. So. sometimes quotes are undervalued, which means that stockholders don't have enough confidence in their prospects. Although, investors like Warren Buffett are looking for companies that are undervalued and buy their stocks, but I think you should have a lot of capital to act like this =)
I was working in London at the time and was long some VOW gamma, almost ATM and mostly by accident (part of a dispersion trade). It was surprising amount of positive PnL for a relatively small position, so it turned some heads. Of course, my boss pretended that he did it on purpose - "And There Was Much Rejoicing". Pretty sure if I had an opposite position, he'd have thrown me under the bus.