I did a casual bike tour through hundreds of miles of Netherlands and Belgium. We wore helmets, obviously.

Not wearing a helmet is inconsisent with having many standards for reflectors and traffic planning. Although someone maybe slightly more careful, falling on a bicycle means a risk for head injuries. Why not take reasonable precautions, including instructing people that helmets do not add safety to anything besides head injuries? They're not a panacea, but protect against certain classes of injuries.

Anecdotally: When I was a kid, an obscured oily patch of road contributed to a fall to one side, head first, and slide for about 10 feet and the helmet I was wearing cracked instead of my skull. Road rash but didn't die or end up with traumatic brain injury.