Why haven't we seen a BBing movie with the cultural impact or "bigness" of Pumping Iron in over 30 years?
Because we see such movies/ documentry's ONCE to make a "cultural impact"...after that, it will never have the same impact. Pumping Iron was a time, a place, Arnold, and the world of pro bodybuilding brought out to a viewing audience for the first time....and there can only be one first time for anything.
Just like Jaws or Star wars will always have the distinction of being in that "time and place"....many movies have been done similiar since, but will never have the impact that they did.