Because your shareholders think you’re chicken when you’re being sane:
What boosts a firm’s stock price, and the boss’s standing, is a rapid expansion in revenues and market share. Privately, he may harbor reservations about a particular business line, such as subprime securitization. But, once his peers have entered the field, and are making money, his firm has little choice except to join them. C.E.O.s certainly don’t have much personal incentive to exercise caution. Most of them receive compensation packages loaded with stock options, which reward them for delivering extraordinary growth rather than for maintaining product quality and protecting their firm’s reputation.
(via Matt Mullenweg.)