Also, laziness/efficiency or maybe constraints that the real world imposes on hiring. It's very hard to effectively gauge skill during a few hours with someone

Also, laziness/efficiency or maybe constraints that the real world imposes on hiring. It's very hard to effectively gauge skill during a few hours with someone or initially during a few seconds with their resume. If you find an effective proxy metric for skill and aptitude (like a degree from a league university) and after applying that simple filter still get a sufficient number of strong hires it will be very tempting to go down that path and save time interviewing. This usually will mean dismissing people with unusual backgrounds.