The original ending didn't test well with their focus group whatever audience, so they changed it. Which... Bad as that is, they are in business to get as many people's money as they can, so it's somewhat understandable. We don't have to like it, though.

It's on the DVD, though, and streaming on this site. It's not the same as the book, but it at least veers a lot closer to it than the theatrical release did.