difference between top-tier/mid-tier guys

What is honestly the difference between guys and top-tier frats and mid-tier frats? There are always some mediocre-looking, socially awkward guys in top-tier frats, and there will always be some very cool, attractive guys in mid-tier frats. In that case, what actually is the difference between the guys? In terms of who they can attract in different sororities, will mid-tier guys only have opportunities to date girls in mid-tier sororities, and top tier guys to top tier sororities (even taking into account the character and attractiveness of the individual)? This has been a question bugging me for a while, and while it may sound very superficial, I do think it is a question that needs answering.