[Benzgirl]

I have a feeling what you have seen is just the ebb and flow that goes through all campuses, and has a lot to do with what is happening in the current environment and the political climate.

Starting in the 1940s, Greek Life had dropped off quite a bit because of the war. It took years for the Fraternities to rebuild. Many students after the war were married (GI Bill paid for school) and had little interest, money or time.
In the 50s, Greek life in general grew, peaking in the early 60s.
By the late 60s, the anti-establishment grew in popularity and many houses closed by the early 70s.
Around 78, things became moderate to conservative again and Greek Life grew into the 80s. It peaked, however, in the early 90s. Again, many chapters closed by the late 90s.
From what I understand, there is a resurgence again.

There is a company that does assessments of Greek Life on campuses, comparing them with like-campuses. I have seen this report on the DePauw and Bowling Green websites, and perhaps on the Lehigh website. If you are really interested in doing research of this kind, you might want to check this out.

If you need some help, let me know and I'll see if I can find the reports again.