“I don’t think that the issue is that these schools have “fallen” in the last 45 years. I think that what has happened is that hundreds of other schools have “risen.””
In several prominent cases I’m aware of, those rises were stimulated by huge contributions to their endowments.
By contrast, according to these links, if I skimmed them correctly,Wesleyan and Brandies seemed to have suffered from suboptimal endowment growth along the way, due to ill-timed expansion strategies and/or sub-optimal endowment investment, use or financing strategies.
http://talk.collegeconfidential.com/wesleyan-university/325337-why-is-wesleyan-endowment-so-low-p1.html
http://innermostparts.org/2009/02/01/did-debt-cause-brandeis-financial-woes/
While Oberlin attributes its rankings fall more to the de-emphasis by US News of the academic peer-review survey
http://oberlin.edu/alummag/spring2007/features/the-numbers-game.html