In a few large organizations where I've worked, there was rapid turnover in the CMO position. In your eyes, is CMO tenure so short because they're not interested in long-term results in terms of customer value, or is it just job churn?
I believe there is more turnover than is healthy in many corporate management positions, not just CMOs. However, marketing is a good deal more dynamic and fluid than many other business disciplines (finance and accounting, for instance) and so the CMO position probably suffers even more from turnover.
Yes, some of it is probably due to the short-termism that is rampant within corporate boardrooms. But if a company were to put metrics in place (like Return on Customer) that allowed it to assess the long-term customer value created or destroyed with current-period actions, then it would matter a good deal less when the CMO changes jobs, because we could hold today's CMO accountable for the long-term customer value effects of his current actions.