To me, this seems as preposterous as asking “if you’re so smart, why are you so bad at playing the violin, or why aren’t you a Hollywood movie star, or why can’t you run a 4 minute mile, or why don’t you have a million Twitter followers?”
Even if we make the questionable assumption that the very concept of general intelligence (something like what an IQ test purports to show) is sensible, why would we assume that it correlates positively with success in any conceivable discipline?