In the final Hobbit movie, The Battle of the Five Armies, why did the movie start with Smaug's death? Why did this not conclude during The Desolation of Smaug?
According to Peter Jackson (source):
We did talk about it a lot. There was certainly a lot of discussion about it. It was just an opportunity. It was just a chance – it’s very rare that you get to do films back to back whether it’s two or three films and to be able to just end on a cliffhanger.
And so it was a deliberate choice to end the second movie on a cliffhanger.
Peter Jackson and Philippa Boyens discussed this at some considerable length in the filmmaker's commentary for the Desolation of Smaug. In short, there was studio pressure to leave the film on a substantial cliffhanger and by resolving the dragon plotline, you'd lose the ability to involve the Laketown characters in the third film, without resorting to flashbacks to explain who they are and why they're fleeing the city:
Jackson : There was debate about the ending, whether we should have a cliffhanger or not, I mean at the end of the day, there wasn't [chuckling] a hell of a lot of choice about it, really I mean, y'know, there was never any talk about destroying Laketown in this film, I mean I think, y'know there was a sense maybe that maybe it's a sort of, this, that Laketown, the destruction of Laketown was going to be the end of the film but in a way it's not, it just didn't feel right to us because it's not, I don't know, it just didn't feel like it belonged in this film for some strange...well we, this was never a decision that we even seriously considered, it was like, well you actually can't end this, with this by....
Phillippa Boyens: ...Resolving everything...
Jackson : Because as it is, you see, with the Dragon attack at the start of the third movie it also gives us the chance to push through some of the other storylines so even though something may happen to the dragon (spoiler alert) the, there was still a lot of other narrative that's motoring on at the same time.