What makes a top tier house top tier?

I see all the tiers listed and am just trying to figure out what makes someone place a house in that tier.

Is it the attractiveness of the members? Because quite honestly I have seen plenty of girls from every house on campus, and I can hardly tell a difference. They all have attractive girls. Is it because they dare to let in some girls who might not fit your standard of beauty? God forbid someone without a perfect body get a chance to experience sisterhood.

Is it the intelligence level of the girls? Would love to see a gpa comparison of the top tiers versus the bottom tiers and see how much better the top tiers are, or arent.

Is it the physical house? Ok, maybe I get this one. But, it is iffy. I see "mid tier" houses that are pretty damn awesome. That ZTA house is unreal. Fuzzy has a nice place. AGD has that stone front. AOPi and DZ look like something out of Better Homes and Gardens.

Is it social events? Not sure about that. Even the "lower tier" places have plenty of events. Maybe they are with the "wrong" frats? I guess if you are going to be a judgmental POS, might as well judge everyone and not just the sororities, right?

So what is it? I see barely any difference at all between these houses. Certainly not enough to warrant the attacks and social stacking that goes on here.

Someone clue me in.