It's the way Hollywood works. Unless you're Michael Crichton or Stephen King, once you sell film adaptation rights, you pretty much lose all control over what happens to the subsequent film. I know of writers who've sold their books to Hollywood and in the final reel, only the title of the book remained unchanged.
I forget which writer from the 30s (Fitzgerald?) said to a younger author:
"when you sell a novel to Hollywood, get out at the California line, toss it over, turn around and don't look back."
(Paraphrased from memory.)