There hasn't been a "Chosen one" for a thousand generations. Have you ever read the Novel, Chapter 21 specifically? - I've only got the german translation, so I must back-translate and it won't fit the original text, but nevertheless: "too old I was", Yoda said, "too inflexible. Too arrogant to see that the old way is not the only way. The Jedi I've trained, supposed to become like the Jedi that had trained me, hundreds of years ago. But those aged Jedi, in another time they lived. Changed the Galaxy has. Changed the Jedi-Order has not. Not allowed it to change, I have." and later on: "The Jedi training is not the only source of self discipline." Anakin was the Chosen One in more than one sense. And one of these "senses" was to make the Jedi realize that their own order and teachings had to change.