Including practice squad players (who are paid peanuts), the NFL has about 2,240 roster spots. About a million US high school students play football any given year. The average NFL career is 3.3 years.
So from 3.3 graduating classes of a million high school football players, you'd expect somewhere around 0.07% to make it into the NFL. Fewer even will have something resembling a successful career.
Then look at how many high paying "smart person" jobs there are. There are about a million doctors in the US, two million engineers, and four million computer professionals.