what determines ranks?

Arrogant fools who believe they are better than others create these ranks, there is no other criteria. there are gorgeous girls in every sorority, and not so good looking girls in every sorority. Stereotyping creates these ranks.

Nothing determines “rankings” other than certain people’s egos.

rankings rarely change. newer sororities start at the bottom and may (very slowly) move themselves up. I would say, if it had to be anything, the sororities with the most v pretty girls are ranked the highest which will always be the top 4 considering thats basically how they recruit. but actually.
reputations persist. alpha phi will always be considered top even with a bad reputation. frats get fixated on certain sororities and dont seem to take risks with lower ranked sororities to mix with, which adds to sororities stereotypes bc they actually get judged based on who they mix with lol.
(i just realized you're talking about rankings on this website---- its literally all self-ranks and hate-ranks, it literally doesn't reflect anything or mean anything)

and also, stop worrying so much about ranks or it'll bite you in the ass. be yourself an find your people.
(but realistically, if you're v pretty even with a bad personality you'll probably be fine considering top sororitys here are shallow af (except for chi o tbh) and don't seem to care if you're dont have much going for you besides your looks)
good luck & trust yourself