Can't call it a reboot because it is a sequel and the plot may generally follow the lines of IV but is different in many ways. And it is an atonement for the horrific prequels first because it did right pretty much everything the prequels did wrong and second it pretty pointedly did not mention or refer to the prequels in any way whatsoever.
I often think that the pre-quels were made the way they were for the expressed purpose of expanding the fan base.
a love interest story for the girls and young women; a "cartoonish" feel and low brow "comedy" (like the Gungan chieftain shaking his head and throwing slober all over) to get the kids interested (read: "Mommy I want that SW's toy!")
I also believe that Lucas did this fully aware that it would piss off core fans and that he may have lost some, but that the financial pay off (I mean just look at the profit numbers in the graph OM put up) and the expanison of the fan base would more then make up for the geeky co-splay fans in the crowd
Never forget, when ep 4 came out, 20th century fox (thinking the film would be a bomb) let Lucas keep the residuals (is that the right term?)-that is, he got the money from after movie sales of knick-knacks,paddy whacks, darth vader masks, action figures and Princess Leia artificial hair buns.
I am sure he was motivated by this need to re-invigorate the toy, masks, coffee mug and co-splay costume market by making a whole new slew of characters endearing to the fans wallets.
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any "necessary" backstory could have been better told in one film-the corruption of Anakin and the creation of the Clone Army was the only thing I found interesting in these movies