Long story short, women switch to catabolism way earlier than men, while they still have glycogen inside their muscles. Men don't switch to catabolism until after they are completely out of glycogen and are creating fucktons of lactic acid. Since your muscles run on glycogen, and lactic acid is not a great thing to have kicking around, women actually appear to have a better metabolism for endurance.
Unfortunately a lot of doctors and researchers are men, and are extremely dismissive of the idea that there is any reason to actually study women, instead inventing behavioral reasons for why you don't always get the same results for men and women in studies.
I think the fact that you are willing to chalk up the fact that women are winning these races on occasion to there not being enough elite runners has signs of a similar chauvanism.
(This is mostly off the top of my head, but I have a degree in biology and I have studied metabolism fairly extensively)