1) The CEO knows something I don't.
2) The CEO is dumb.
Those are rarely it. The third one is:
3) The CEO is optimizing for personal wealth / fame / success, and there are political considerations.
Most CEOs can recognize that a business decision can be absolutely the right thing to do for the business and not make that decision if it either would cost them (1) their standing with shareholders (2) their annual bonus (3) their standing with the board (4) their standing with internal constituents.
The key skill CEOs need to be CEOs can be summarized as: "How to become a CEO." That involves a lot more management of politics than it does business success (but still a fair measure of both). Furthermore, if a strategy leads to business success but costs a CEO their job, they cannot take that strategy.