John Williams left. He was not fired. I've read speculation that if Williams starts to sense a movie he is on may flop, he leaves it. Movie studio execs are pretty narrow minded and if your last movie was a flop, they blame everyone involved whether it was their fault or not. John Williams is a very wise man and knows box office success means he gets hired more often. He was also "replaced" on THE SENTINEL (1977) by Gil Melle and there are probably a few others he bailed on, not that I blame him.