Why is Cheney breaking tradition by not running for President?

For the past half century, the VP has run for President after the President's term is up - Nixon from Eisenhower; Johnson (sorta) from Kennedy; Humphrey from Johnson; Ford from Nixon; Mondale from Carter; GHW Bush from Reagan; Quayle from GHW Bush; Gore from Clinton .... So what's up with Cheney? Certainly he doesn't think the American People are smart enough to see his run for President as a grab at a 3rd Presidential term? What else do you suppose he may have in mind? If the Republicans can let/encourage someone like Quayle to try it, why not Cheney?