Because money, that's why.
Erik posted last week that Peter Jackson was thinking of turning The Hobbit into a trilogy of films. Today, Jackson made it official. His reasoning for taking a kids' book that runs a little over 300 pages, and stretching it out to fill three films (at two-and-a-half hours apiece) is thus:
It is only at the end of a shoot that you finally get the chance to sit down and have a look at the film you have made,” Jackson wrote. “Recently Fran [Walsh], Phil[lippa Boyens] and I did just this when we watched for the first time an early cut of the first movie — and a large chunk of the second. We were really pleased with the way the story was coming together, in particular, the strength of the characters and the cast who have brought them to life. All of which gave rise to a simple question: do we take this chance to tell more of the tale? And the answer from our perspective as the filmmakers, and as fans, was an unreserved ‘yes.’
That sounds nice-ish. But c'mon. Warners & Jackson are taking the appendices from Return of the King, and shoving them into The Hobbit like John Madden pounds birds into other birds at Thanksgiving, and they're doing it for one reason: the one stated at the top of this post.
That doesn't necessarily mean the films will be bad. They might be great. But I've noticed that when Peter Jackson is forced to be economical with his storytelling, he can make miracles (Heavenly Creatures, The Fellowship of the Ring) and when allowed to indulge, he splashes around in emotionally sloppy puddles of cinema like King Kong, and The Lovely Bones.
Maybe he'll reverse that trend with these three films. Or maybe it'll be a 9 hour long feast of overcooked Middle Earth Turducken.