Its because the book is alot bigger than the previous ones. I can see the benifits of splitting it in two parts as it allows the film makers to stick to the book without missing any out.
Personally I wouldnt fancy sitting through a four hour film. I did it for the Lord of the Rings when my local cinema screeened all four back to back and I will not be doing it again. So I think Milked is the wrong word, if they had tried to condise it they would have got critisim for missing out parts of the book.