My understanding was that the Jedi were too arrogant to understand what bringing that "balance" would mean, ascendancy of the Sith, the Empire, the near-extinction of the Jedi etc.
Then in the end, we're left with Luke, who was a more human and less aloof Jedi. (Never read them, but my understanding in the EU is that he married some female ex-henchwoman of the Emperor turned good, and had Jedi kids, whereas the Jedi before were purely monastic and recruited only from without. And Anikan rebelling against that with his secret marriage to Pada... Panam... Panda-bear whatever her name was (Robot Chicken FTW!) and the fear of her loss that turned him to the dark side.