Philippa Jane Boyens MNZM (born 1962) is a New Zealand screenwriter who co-wrote the screenplay for The Lord of the Rings series, King Kong, The Lovely Bones, and the three-part film series The Hobbit. (wikipedia)
As a screenwriter, you have to let go, and you have to hand your baby over and let it go off into the world, which is entirely appropriate.
It is hard to go back into a world that has already been explored, so to speak. And the fans are very passionate about it, and you don't want to burst that bubble; you don't want to break that illusion. You want to get it right. You want it to feel familiar, but also surprising.