| because what makes a good movie and what makes a good book are very different. in book time is not an issue you can put the book down and read it again, plus its all words and you using your mind to exstaperlate what people, things, and places look like.
in movies the audience is useing their site, it is a visual media, you see what the people look like, there is music, and well the whole shanbang is different. yoiu have to convey the same story, that in the book may take two months to read, in two hours. thus you have to remove things to make it a better movie. the fact is movie maker are not making a carbon copy of the book, they are telling the same story in a different way, it is impossible to make a movie that the book is the script, if people did that, the movies would stink, plain and simple. now somtimes the book is better than the movie, and the movie is better than the book, some books can't be made into good movies.
though i do not know the movies you are talking about, it is highly probable the director, and the screen writer, felt it nessasary to make the changes they did. maybe they were not good changes, but remember they were trying to make a good MOVIE, not a visual copy of the book. | 
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