Personally I believe that when Star Wars became a massive hit, Lucas lost the run of himself. Suddenly he could make sequels that weren't low budget, weren't novels etc and I think he got so excited that he started thinking and talking about sprawling sagas over 12 films, then a film every 2 years with different creative people behind each one, then backstories and future stories, none of it really being planned out. It was just Lucas' imagination firing as he thought about what he could potentially do given the massive success of Star Wars, rather than a master plan that went beyond three films and maybe a prequel. I don't see how this is a problem, considering that Lucas went on to make five other outstanding SW movies. They weren't perfect, but what movie is?