I'm not confident that your observations are an accurate representation of what the truth is.
First, what bikers were you observing? What time of the day was it? Where was it? Who were they?
Club riders will always wear a helmet as most clubs force it, so you have probably hundreds (thousands) on any given weekend active. But you won't see most of them because many of the rides take place outside of the city.
Tourists visit, rent a bike for an hour on the Greenway and skip the helmet because the perceived low-risk of riding on the path and $2 helmet rental/charge.
Delivery guys, often on Mtn bikes, are now required to wear company-funded helmets. I'd say that more than half wear one
Couriers, often on single speeds, are in their own group.
Recreational riders, on the whole, don't wear a helmet. I've seen many have their helmet strapped to their handlebars, in their basket, on their backpack, etc. Maybe they are omnipotent or maybe they don't know any better.
Commuters are a seasonal group. At my company there are probably 40+ people who commute in the warm summer months. All but one that I have seen wear a helmet. Many don't have lights as they only travel during the day time. For the ones that do travel at night (maybe 5), most seem to have clear white blinky up front and a red blinky in the back.
Now that we're into the shorter and colder days, there are just two people who commute regularly, but these two people both wear a helmet and both have HID or better lighting systems. I think only one posts on this forum
