affect of admissions on rush

[TechTransfer]

I work for the university archives, and today I was very bored, so I decided to start playing with the yearbooks. I noticed that fraternities appeared to have been significantly larger in the past, and again, being bored, decided to start counting. I noticed a marked phenomenon in the 1990s:
Year: Total Greek men (number of chapters) [average chapter size]:
1990: 755 (12) [62.9]
1992: 698 (11) [63.5]
1994: 578 (10) [57.8]
1996: 514 (10) [51.4]
1998: 452 (8) [50.2]
2000: 422 (7) [60.3]

Before 1990, it had been a slow but steady increase through the 70s and 80s (from about 600 to about 800), and since 2000 it's been a very slight rise, up to about 450. The increase in the 70s and 80s makes perfect sense, because the student population was increasing during that period, but we've held steady at about 9000 undergrads since 1988. So what explains the drop in the 90s? The system lost 11% every two years on average.

Extra fact: in 1991, we implemented selective admissions. Before then, to get in all you had to do was graduate high school. In '91, the school implemented admissions standards for the first time, and has been gradually increasing them every year since- the bottom third of students admitted in '91 wouldn't get in now.

My theory: The fraternities didn't adapt (and still really haven't) to the higher academic quality of the students. Someone who got a 38 on their ACT is looking for something very different out of college than someone who just barely graduated high school, and as the average student has become the former rather than the latter, they haven't adapted their programs.

Why do I care? Partly because I see a niche for my group, and partly because I'm thinking about writing a paper on this.

Has anyone noticed this at other schools, or is it just us?