We are not as exchangable as the people who work on movie sets like key grips or boom techs.. We have technical/artistic skills that go beyond the average film set worker.
I would suspect they feel the same about your or other industries. Any time you specialize in a field, you know the ins and outs more than someone outside it. No matter what the field, people outside it always tend to think "oh, is that all they do all day?".