Masters but not Commanders?

Interesting note from Tom Ricks about how "so many eligible Air Force colonels were declining to be considered for command that the Air Force chief, Norton Schwartz, issued a letter in 2009 saying that henceforth everyone would be considered." Being a commander is a tough job, to be sure, but it's also a prerequisite to getting a star. I have no special insight into the reason behind the problem, but it may be because by the time you've made O-6, you probably know whether you still have a chance to be a General. If you don't, why put yourself through the heartache of being a commander?