@liztai it gets changed for the following reasons:
1. It's an adaptation, and they can't film the original scenes for some reason (usually budgetary)
2. Successful filmmakers believe they can create better than anyone else. They 'know' what this work needs. This includes notes from studios, some of which are chasing the dragon and make little sense. Like people are wearing hats. We should include more hats in our work.
3. If you make a change, and that change is successful, it will boost your career. So everyone with the power will tinker as much as they can, so they get known. 'Ah, so you're the one that had all the chipmunks wear filbys in Chipmunks Go Wild.'
It's a cutthroat business. Everyone's trying to gain an advantage so they can get larger fat wads of cash and prettier PYTs.
My 2c.