If you turn in a drivers license because of dementia, do you need to tell them the reason?

We didn't just turn in Mom's license. When it was ready to expire, we asked them to change it to an ID card (which doesn't expire). There was no problem, and everyone needs to have a picture ID. It looks like a driver's license for the most part and we used it without question for airline flights and any other time she needed to identify herself. It's been more than a few years, so I don't recall anyone at DMV asking the reason, although I might have told them. It was obvious she was aged.

We did the same for my aunt. Just didn't renew the license and got an ID instead. If you wait until after the license expires it's a little more trouble to get the ID. It's best to apply before the license expires as a valid license confirms residency and citizenship etc.

You do not need a reason, nor to state one. All you need is to go to the DMV and get a state ID. My mom decided she no longer wanted to drive in her early 80s. She was never a confident diver, and no longer wanted to drive.