The author actually argues that one of the reasons is "the bible isn't funny"?
My own guess would have to do primarily with nepotism and secondarily with the appeal of a different perspective of a foreign culture to an American audience. Whether people like it or not, the Jews actually have a strong lobby in the entertainment industry, and they like nepotism, probably even more than the average american.
I wouldn't underestimate the influence of the Borscht Belt. Successful Jews in entertainment vacationed there, while young up-and-comers performed in the comedy clubs. Who got seen? Whose names got circulated around? It was a self-perpetuating cycle until the Catskills clubs fell out of favor.
