It is true that all of world history is data, but it is not necessarily data that can answer any particular question. The problem is the age-old nature versus nurture debate. Both genetics and environment are important to IQ. Both generally affect IQ through long, convoluted, and poorly understood reasons of cause and effect. Therefore we can establish evidence of differences, but can't necessarily distinguish between theories about the causes of those differences.
What would make a difference is a theory of mechanism. For example it is uncontroversial that people with ancestry from Nigeria are better at sprinting, and people with ancestry from Kenya are better at long distance running. For this we can identify specific facts about body type that help with sprinting versus long distance running, and we can identify strong evidence that these body type differences are due to genetics.
But we have no such theory of mechanism that can be applied to IQ. And therefore the mass of data we have about the existence of differences does not distinguish between potential causes of said differences.