First, there's selection bias. We would only take guys that were really sociable, somewhat hard working, competitive, and with decent grades. Most fraternities were the same. "Frat bros" being meathead rich retards is a myth. We would pick the smartest, most promising, and sociable guys in the school. Money wasn't a factor. Neither was skin color, my house was probably 40% minorities. But we had a fraternity GPA a solid .6 above school mens average and a dropout rate of less than half. Fraternities ARE elitist and I was proud of that. So are all the tech companies.... We only took the best. Yeah we drank more than most students and had crazy parties but we were also smart, hardworking, and had a lot of friends.
Second, the power structure closely resembles the business world, complete with budgets of over a half million even in a modest sized house. Bigger houses have budgets of millions a year. These budgets were handled by the "exec board" which was just democratically elected student members.
A fraternity is basically a non-profit company run by students. Harder to do than it sounds, especially with all the hate towards Greek coming from the school itself. At many schools the Greek system is actively shunned by the administration.
Then there's the connections. Being in a fraternity/sorority means you automatically know over 50 people pretty well, sometimes hundreds. I was vice president for several years and I knew hundreds. Maybe 20 really well. I knew people on the school board. I met the president of the University enough times that he knew me by name. The president of the student senate was a great friend that lived across the hall.
I got my first job from an old friend from the house and another was kind enough to help me move across the country to a tech hotspot. We're all still friends to this day and we joke about how wedding are largely a fraternity reunion. Everything in my life today exists largely because I joined a fraternity 8 years ago.