[YawningAngel]

Not that many people do ultra-endurance races, so you're not reliably getting the top of the curve. Variance is high as competitors frequently don't enter (they can't race all the events as they're too demanding) or drop out due to injury/ill fortune. Male muscle mass is not really an advantage in an event wherein the primary goal is to sustain a low effort for a very long time.

Those are a few of my guesses.