Cycling fatalities still make up a third of total traffic fatalities in the Netherlands. And almost 70% of those several hundreds who die in cycling accidents are over 65, people who are much more likely to lose their balance and are more sensitive to an impact, meaning a bit of protection would have gone a long way. That's just fatalities, think of all the non-fatal accidents, and how may of the 6000 people hospitalized each year just for unilateral accidents (with bollards or lamp-posts) need an MRI because they bumped their head. The numbers don't get better without adding protection because according to SWOV almost 80% of cycling accidents are unilateral or between cyclists.

But there's a cultural opposition to helmets in many countries, chief among reasons being that "helmets don't look good" and "real cyclists don't need one". If you didn't wear one your whole life, you won't start at 65.