artemis

There are a few reasons to consider. Movies generally want the largest audience they can get because the studios behind them want to make the most money. In order to maximise profits, studios tend to:

-cut parts to keep the time down.

-Change the book to make it more understandable to more people. This is often called "dumbing down" the material.

-take out parts that might be offensive to a larger audience.

-modernize the movie to fit a modern audience with music, characters, pace.

Generally, movie versions of books are disappointments to readers of the book but there are some exceptions.