Well, in all fairness, in order to filter out references to all the other Wesleyans with state names in front of it, you have to use the definite article. But, if you remove Wesleyan from the mix entirely (and, substitute Swarthmore), you see a similar result with Amherst,Williams and Oberlin cresting in the mid-60s then gradually levelling off until pretty indistinguishable from other top LACs:
https://books.google.com/ngrams/graph?content=Swarthmore+College%2COberlin+College%2CHaverford+College%2CDavidson+College%2CAmherst+College%2CWilliams+College%2CPomona+College%2CBowdoin+College%2CCarleton+College&year_start=1945&year_end=2008&corpus=0&smoothing=3&share=&direct_url=t1%3B%2CSwarthmore%20College%3B%2Cc0%3B.t1%3B%2COberlin%20College%3B%2Cc0%3B.t1%3B%2CHaverford%20College%3B%2Cc0%3B.t1%3B%2CDavidson%20College%3B%2Cc0%3B.t1%3B%2CAmherst%20College%3B%2Cc0%3B.t1%3B%2CWilliams%20College%3B%2Cc0%3B.t1%3B%2CPomona%20College%3B%2Cc0%3B.t1%3B%2CBowdoin%20College%3B%2Cc0%3B.t1%3B%2CCarleton%20College%3B%2Cc0