Higher IQs have huge correlation with neuroticism.

As in, most of them are crippled with mental illness and various emotional disturbances to a point where their IQ is basically the only thing that keeps them useful in society, and often times not even that.

In the same way the lowest IQs are usually superhumanly strong and good at simple labor (if they aren't also physically deformed), nature has a way of balancing us all down to equals generally.