Many fans growing up watched the OT for Han Solo, because he was so cool and got attached to that character. Many fans, mostly females, loved Leias feistiness and got attached to her for 3 movies. Many fans like myself wanted to be Luke Skywalker from the minute he leaves Tatooine, not cause he is a jedi, just cause ANH was about achieving bigger things in life, and Luke achieved that at the end of the movie.
So now you watch the saga 1-6, and you are one of those fans who never fell in love with why Darth Vader came to be, cause you thought he was cool, but being a bad guy is all he ever was to you. No matter how great or crappy the movies are made, what characters can you follow for 1-3? If you follow Padme, she is dead by Episode III, and is only mentioned once in 4-6. What Lucas forgot by making this a linear story of Darth Vader was that ALL of the characters in the OT was just as key as the mythology, action, and special effects, and by making the saga solely about Anakin forces the viewer to really love his story for 6 movies, and if you do, I guarantee you are a saga fan.