This whole thread including this comment feels like people who haven't ever been to The Netherlands making suggestions that make no sense for the cycling culture here.
So firstly as has been covered in other comments here, cyclists in The Netherlands don't want to wear helmets for their daily commuting, it doesn't solve any sort of safety problem for them when you factor in the inconvenience they cause.
Secondly even if they did most bicycle chains here are over an inch thick, not something you can thread through a bicycle helmet.
Sure you could carry some extra wire just to lock the helmet to the bike, but that gets you even further down the road of making a bunch of special accommodations to solve a problem that doesn't exist in the first place.
>cyclists in The Netherlands don't want to wear helmets for their daily commuting, it doesn't solve any sort of safety problem for them when you factor in the inconvenience they cause.
This sounds very much like "I don't wear my seatbelt for commuting. It doesn't solve any sort of safety problem when you factor in the inconvenience it causes."
Let's say there was a country where 0.5% of the drivers used seat belts[1], and out of those mostly just race car drivers. Yet that country had no notable increase in injuries or fatalities in car crashes as a result compared to countries where seat belts were mandatory.
Add into that that in this parallel universe driving a car daily had big long-term health benefits, and the introduction of seat belt laws in other countries had caused driving to drop by 1/3 [2], causing fewer people to cycle, overall health to decline, and a reduction in car safety due to less car safety in numbers. Since a major cause of accidents was that few people used cars daily, leading to accidents where people weren't expecting them.
Then yeah, I think it would be completely fair to question whether wearing a seat belt in your car was worthwhile. But of course none of this analogy makes sense, which makes your argument rather nonsensical.
So firstly as has been covered in other comments here, cyclists in The Netherlands don't want to wear helmets for their daily commuting, it doesn't solve any sort of safety problem for them when you factor in the inconvenience they cause.
Secondly even if they did most bicycle chains here are over an inch thick, not something you can thread through a bicycle helmet.
Sure you could carry some extra wire just to lock the helmet to the bike, but that gets you even further down the road of making a bunch of special accommodations to solve a problem that doesn't exist in the first place.