For one the IC basically excludes edgier and free spirited types, or those with baggage, by design. It also excludes financially motivated people and academic types - in practice we’ve already ruled out most of the urban upper middle/upper classes and most poorer people. Among the remainder you have to pick those with college education that are willing to live in or around cities. And then among those, people willing to commit to a long career, believe in the cause, maintain discretion, unlikely to fall off the wagon… and without any kind of concerning overt bigotry. Besides people who enlisted directly out of high school I feel like Mormons are the only major group who would consistently fit the bill.