"A Film By credit is ugly. It is ego. It is elitist and excludes all the people who work hard on a movie." - Unless no one else worked on the movie.

Concur, Jon. "Directed by" is a plenty fine credit. They should be satisfied enough with that. But this has some historical roots in the whole auteur theory that arose in the 50s. And as we all know, once anyone has established a power position, it is hard to get them to back away from it.