1) it's way more expensive,
2) the loss is gradual and they adapt to a quieter world, or
3) they don't know what they can't hear.
She thought the big reason might be #3. She knows her hearing isn't good (too many childhood infections in one ear), and she related a recent experience. She went to a movie and sat with her husband in the back of the theater because that's where he likes to sit. Then, she went to the same movie with someone else and sat in the middle. She was amazed at the things she could hear that she had missed the first time. Nothing like good anecdotal evidence to validate my theory.
On a new, but somewhat related subject. Is anyone else bothered by television shows where the dialog is difficult to hear, but the commercials blast you out of your chair?