the audience is the controlling factor in the actor's life. It is practically infallible, since there is no appeal from its verdict. It is a little like a supreme court composed of irresponsible minors.
Making a film is so hard that if you don't have your main actors going along with the ride with the rest of the crew it can make your life very difficult.
People want to see realism in action now. People want the actors to perform than the computers performing. Though I have done both, I enjoy the realism of action more.