The Hobbit didn't make it because it wasn't that great of a movie. A movie should be nominated based on its merits, not just because it's attached to the Lord of the Rings franchise, and to be honest The Hobbit didn't have that many.
The second half of the film was good, but the first half moved so slowly and was so bogged down that I wondered whether I'd make it out of the cinema alive. It was utterly boring.
It just wasn't a great movie. Certainly not Oscar-worthy by any stretch of the imagination lol
EDIT: Also, every single dwarf character in that entire movie was annoying to the point of distraction. I guess that's the book's fault moreso than the movie adaptation, but it doesn't help things. I hear some of them die in the next two movies and I'm looking forward to that so much. Maybe those movies can be nominated for Best Picture!