3. It Could Change The Focus of the Story
The Hobbit book is one that plays out entirely through the point of view of Bilbo Baggins. It is about his journey into the unknown, how the quest changes him and also how his relationship with Thorin Oakenshield develops and changes because of this. I believe that for this reason a movie version of this story must keep its focus primarily on Bilbo. I would argue that Frodos plot in The Lord of the Rings is an important part of a larger story that is told from different points of view and so therefore it works in the Lord of the Rings to expand the sections without Frodo present, especially when his quest starts to slow down the pace. While I appreciate this adaptation will follow Gandalfs parallel quest, adding further scenes that do not include Bilbo (as I assume they will) would tip the balance of the story away from being about his character.