why do you guys care about rankings so much?

Well, to start with, who are you? What is all this to you? Are you part of our community?
I'm asking because if you were in a competitive fraternity or sorority you'd already know the answer.

It shows who people think are actually improving and who isn't duhhhhhhhh

I mean, this site is literally called Greek Rank. That's what this site is for.

In every house, there are going to be a few people who are obsessing over the rank, but most people are just having fun.

If you're 'just doing research' then don't come on this site. Like someone else said this is for our fun. There are links on the Greek Life website that will take you to the websites of all the individual fraternities and sororities.
As far as rankings, that has to do with the groups themselves and not any particular individuals. You can find a LOT of individuals who would fit in with ANY fraternity or sorority and not stand out.
The 'rankings' have to do entirely with superficial standards (which we all like and have fun with) like good looks, athletic success, involvement on campus, strength in recruitment.
In practice, the top ranked fraternities and sororities socialize with each other just like the bottom fraternities and sororities socialize with each other. If you join a bottom ranked fraternity, that means your chapter will never have the chance to socialize with a top sorority, but that doesn't mean that YOU are prevented from socializing with girls in ANY sorority.