Hello ,

You need to first understand the responsibilities of the professors at the IIMs , see the first thing is that when a B-school is producing exceptional students , which are getting placed in the top companies all over the country or in some case all over the world , with a very high packages and even many of them have become successful enterpreneur and big buisness men , so if this all thing has to happen then the backbone of this all achivement is the professors of this colleges , the professors from this institutes are themselves very successful , skill full and have themselves done there education from top universities and are expert in there field , so now you might have understood why the professors in IIMs  earn so much .

Hope it helps ,

Thank you