1) Race isn’t a well-defined variable. It’s socially-constructed. Example: Italian-Americans have not always been considered white. And many people are mixed race.
2) Intelligence isn’t a great metric either. I’m not even convinced it’s a single number. There are people who are great at maintaining dozens of relationships, and can remember things about each person. There are people who are killer at problem solving. And there are people who have uncanny kinesthetic coordination. Which one is more fundamental to human cognitive tasks?
3) Distributions. What do we care about within a population? Is it the mean? That tells us nothing about how skewed the population is. Is it the median? There are problems with that as well. The population could have a bimodal or multimodal distribution. Then what?
4) Confounding variables. You know what’s a lot easier to measure than IQ? Money. Unfortunately a person’s quality of education is highly correlated to the wealth of their parents. And so is stress, which knocks down IQ as well. And there are a ton of other confounding variables too that I don’t know about because I’m not a social scientist. If you do a straight-up tally of IQ you’re not necessarily even measuring anything cognitive at all.