Because that is where people specialize. If we ranked all humans by their programming skill and see which ones choose to become programmers, you'll find it is

Because that is where people specialize. If we ranked all humans by their programming skill and see which ones choose to become programmers, you'll find it is all around the tip. The average programming skill of the average programmer is far greater than the average programming skill of the average person. This applies to innate talents as well. People go into careers based on what they are good enough at. If you are literally average or below average at your field (compared to all people, not just all people interested in your field), your chance of success is extremely low. Therefore, if on some metric, you have two groups who are average but one with greater deviation, and then you select among the top 5% of the combined group, you will select more of the group with greater deviation even though the groups are average. You can test this with simulations if you want. This isn't much of a problem until you apply it to everyday demographics, at which point it can result in uncomfortable conclusions.