Speaking for myself, I place quite a high value on my brain. I'm vain enough to think it's a specially good example of its kind. So were I persuaded that wearing a helmet made a material difference to its chances of surviving or avoiding injury, I'd certainly wear one.
But I'm not. For anything other than superficial injuries, helmets appear to be an irrelevance. No more essential than elbow or knee pads. I don't wear them, either.