Directors simply got ratings.
You make an interesting point. It seems no matter how low Coppola sinks, you can't take away Godfather, Godfather II, The Conversation and Apocalypse Now. If Lucas is being punished for the Star Wars prequels, why isn't Coppola downgraded for Jack, Twixt, One From the Heart, Youth Without Youth, Gardens of Stone etc.? I Rated Coppola a 6 and Lucas a 7, and I'm the only person to rate Lucas higher. (PeacefulAnarchy rated them both as equals.), so I'm interested in reading some response to this.