That's easy. There are three reasons:
1. English has an obscure object of discipline. 'Hard' sciences and even social sciences seem (at least to outsiders) to possess relatively clearly defined objects of 'expert knowledge.' Moreover, what they do tends to have much more direct material and ideological relations to capitalist production, social reproduction, and legitimation than the study of English does. What are these things called literature, culture, art, or worse yet, 'discourse'? Who can define them? And if you can't define them, why create a discipline that does not have a clearly defined object of study? (Is it some kind of con game?) And even if you can define them, do these things really matter? Aren't they mere luxuries--elitist hobbyhorses that do not affect our lives one way or another? Why should anyone get paid _at all_ for pretending to be an 'expert' on nothing?!
2. Most people think of tenured English profs--esp. stars--as leading lives of leisure appropriate for men of letters of yore. (In pop-media imagination, they just don't seem to _work_ at all.) Even those who _know_ that profs do put in long hours may think, "wow, those English profs can make a living by reading novels/watching movies and writing about them! God, what a life!" The English Dept. is now a symbol of what ordinary workers are denied: the chance to combine paid employment and hobby. Hard to believe, Jamie, but tenured English profs have become "that obscure object of desire." Surreal.
3. On top of all this, English theory-heads dared to develop an 'insider language' burdened with Jargon! You know, it's ok for physics profs to have such a language, because they are legit experts of a proper (if arcane) body of knowledge. Besides, if we question their Jargon, we might end up looking like know-nothing idiots! But for English profs to not speak English! (We must make English the official language of all the English Departments in America!) After all, all of us speak English, so all of us should be able to understand what English profs are saying without making a Continental detour. Last but not the least, Jargon merely allows them to _hide_ the fact that we are not really 'experts' of anything (see the Reason 1 explained above).
In short, academostars in English are a problem because, for both better and worse, we are not really seen as legitimate experts or professionals of any kind. For further examination of the subject, see Bruce Robbins' _Secular Vocations: Intellectuals, Professionalism, Culture (London/New York: Verso, 1993).
Yoshie "Help!--I got 100 papers to grade this week!" Furuhashi