leah herself doesn't know why. it was discussed in BD, when she's talking to jacob. i don't have my book with me, so i don't know.
yeah, i know there's gonna be a book from nessie's point of view. but i don't think she deserves it either. honestly, her character just isn't developed enough to have it from her POV. we already KNOW jake, we just want to find out how he turns out. personally i think the focus needs to now move WAY AWAY from bella and edward, and directly onto jacob and nessie for that to work out, and therefor i think while their story needs to be told, it needs to be told from jake's perspective. besides, that's way more interesting.
leah is great because she is strong, yes she makes mistakes, but at least she stands up for herself and what she believes in, even if the others think she's being silly or even witchy. and since she's so intelligent, and so insightful, she's usually right in what she says.
it's kind of ironic, because i think emily and leah, besides alice, are the strongest female characters in the books.
death cannot stop true love, it can only delay it for a while...