And your contention is that “Asians and Jews got more of dem good genes” or something? What genes do you think are involved? Why would any gene that unambiguously conferred greater intelligence not reach 100% penetrance in human populations?
Why are isolated populations differently endowed? Because they face different challenges and, by chance, often arrive at different solutions. That's at the heart of evolutionary theory.
That aside, one can simply observe the differences and try to come up with alternate explanations. Granted, observing genes is no easy matter...but we're getting there.