Some perspective from a writer who has also narrated quite a few audiobooks:
A narrator takes the story you, the author, created and runs it through his or her body at a word-by-word, second-by-second, level. That's an intimate thing. Literal. Physical. Tactile. It has to be that way because an audiobook is an intimate experience for a listener, as well. When a listener hits 'play,' he or she will have the experience of a soft voice in his or her ear for hours on end. How many actual humans would you allow to stand about six inches from your body and whisper into your ear for hours? Not many, I'm guessing.
Narrators who do a great job are living your story and bringing it alive for readers. That's no small thing.