Earlier quoted context omitted.
Wearing a helmet in your car would prevent a lot of injuries as well, and nobody does that. This is just a risk/reward trade off and I (as a Dutch cyclist) feel a few additional deaths on the total population is not worth the effort. And the things are uncomfortable and impractical: what are you going to do with it when you arrive on your destination? Lug it around all day? Bring a bag everywhere?
Don't you carry a bag around already? If your commute is one hour cycling in guessing you might sweat and need a shower? I cycle to work (in the UK, similar climate I guess) for about 15 minutes each way with no steep roads and I gotta be very careful with my pace if I don't want to sweat.
1. The weather is Holland is kind of optimal in maximizing not sweating.
2. We are not going that fast. The effort we put into it is identical to a normal walk. You just go three times as fast.
The difference between walking/running. Which is why you don't need a shower and why you don't need a helmet. So you go about 15 km/h at most. The bike is heavy (giving you much more stability). You sit up straight (giving you a much better view). You stretch your legs and you are standing still with a bike between your legs. You don't fall with a bike a holland, you loose balance and choose to stand.
For all intents and purposes, its just like walking and every non-dutch person keeps coming at it as if we are doing sprints or a marathon.