national awards

One reason for this is that the "old ladies" care more about things that frat guys/other college students don't care about and vice versa. On campus they might be known as the hottest, but it is always possible that the same chapter preforms poorly nationally when it comes to community service and other involvement.

Winning awards often depends on how strong a sorority is nationally. When you are competing against a larger number of chapters who generally are the better houses on their own campuses, it is much harder to win national awards.

The Odyssey has a list of the 10 Best National Collegiate Sororities, and it's pretty similar to any other list you'll find. It includes Chi O, Zeta, Tri Delt, Theta, Pi Phi, ADPi, KD, and Kappa. These houses have way more competition when it comes to winning a national award.

Two houses that have less competition because their sorority isn't as strong nationwide? Sigma Kappa and GPhi.

just to fact check the comment above -
ADPi - 155 chapters
KKG - 140 chapters
GPhi - 140 chapters
Sigma Kappa - 125 chapters

Yes there is a difference but not by much. If there were was a difference of 50 or 60 chapters I would say yes you are correct but the biggest gap is between SK and ADPi by 30 chapters. Yes it is slightly easier for SK to win awards than it is ADPi but when you consider that SK here is competing against 124 chapters and manages to snag 4 awards where Adpi goes up against 154 and can't even get one you clearly see that ADPi must not be doing so well. If SK won 2 awards and ADPi won 2 awards I'd say that ADPi would be better when you consider the chapter gap, but as of now Sigma Kappa is clearly better nationally as well as GPhi compared to KKG.

Check your facts before you try to make good chapters look bad.