Put Simply, Disney did not allow for the final few episodes to be created. The only Episodes that Disney allowed for release were the ones that had already been created. The whole Clone Wars Series was meant to be longer that 6 Seasons... This is the reason for so many "missing" links as it were.
They then obviously had to find other ways to finish stories, comics is one of the more open ability ways of doing so... makes sense that they would use the opportunity to satisfy the die hard fans. After all, all who saw the link Lummy put up a while ago will have seen just how much they had fans in mind when creating the series :)