Why did they change the book to make the movie?

Flavorwire did a great article on some authors feel about the movie adaptations of their books.  My personal favorite is:

Richard Matheson on 2007′s I Am Legend, the third film adaptation to be made in his lifetime, and the third that he didn’t like:

“I don’t know why Hollywood is fascinated by my book when they never care to film it as I wrote it.”
 

Love it!!!!!!