That may have to do with him having grown up around it and probably hearing about it from his father (I'm not familiar with ages of his children and how close he was to them). He probably has this image in his mind of the books and stories from his father that he probably would not want tarnished by the movies (although I will admit, as a big Tolkien fan, I was dazzled by the movies and how close they were to the books with the length they ended up being).
I honestly believe that Christopher just can't imagine that the story can be captured to any extent in a visual interpretation. I would like to see if anyone can get the Shire scenes to him at least just so he can see what Jackson is capable of.