what are sorority rankings actually based off of?

I would assume that any ranking of top houses would be based off of how well each house exchanges, but the generally accepted rankings on this site don't reflect that. For example, this site says SK is now below AXO and AOPi, but they exchange way better than either of those houses. Also, apparently Theta is above Tri Delt and Zeta, but the only house that exchanges worse than Theta is G Phi. Rankings also can't be based off of return rates during recruitment because PHC doesn't release that. So are these rankings just girls in sororities deciding how much they like other girls in other sororities? Which brings me to my next point: who the hell cares?