Wait, men fake orgasms?
salon.com
salon.com
Not sure the exact reason, maybe something to do with the brain turning off pleasure / pain receptors? Achieving an orgasm will sometimes just not happen unless you exert a huge amount of focus and concentration.
I had done some informal surveys with people who take the same sort of pounding on their bodies: stunt people, professional football and hockey players, UFC fighters. But none have admitted to having the same issue.