Trivia: The first live adaptation film of The Hobbit was made by the Soviets for Leningrad children's TV in 1985. It is on YouTube: https://youtu.be/v7Sab9LgUxg.
Trivia: "Bombur" doesn't have a single line of dialogue in the movie.
Trivia: In addition to reprising his role as Gollum, Andy Serkis served as the second unit director for the trilogy.
Answer: Gandalf has already convinced the dwarves Bilbo is a burglar and Bilbo realised he needs a lot to convince them otherwise. Bilbo is also intimidated by Gandlaf and confused about his claims so he is not sure how to handle the situation.
lionhead