There is a difference if you fall off a bike moving at 30km/h or fall down while walking.
In the Netherlands the risk of using a bicycle is probably vastly lower than elsewhere. All cars are used to bicycles being everywhere. Most drivers probably use bicycles, too.
There are tons of bike lanes that are physically separate from car lanes. Etc. So one could argue that the risk of a severe injury from riding a bicycle is so low that you feel it's ok not to wear a helmet. Clearly most dutch people think this way.
Exactly. There's also a difference between falling off a bike at 30km/h or at 15 km/h (a common bike speed for most people). And there's a difference between falling off a bike and falling down the stairs.
There are always risks, different ways to mitigate those risks, and trade-offs around those risks and mitigations.
Not all bike accidents involve cars. Sometimes people hit rough pavement and wipe out all by themselves, and it's quite possible to hit your head on concrete or asphalt when this happens. Humans didn't evolve to handle hitting their heads on rock-hard surfaces at high speeds; we evolved to walk around at very low speeds, and not generally fall in a way to hit our heads on things (because primitive humans were walking, not riding mechanical wheeled contraptions that kept their legs trapped).
I don't think it's the reach itself, but the fact that we're trained to look in the side mirror before opening the door. And are generally aware of the fact that bikes exist. That last one is pretty fundamental in all aspects of traffic safety.
I mean, Australian drivers are generally aware to check for kangaroos, but American drivers, not so much. The more of something there is, the more traffic awareness of it there will be.
FYI most people don't actually do that in the Netherlands. I know people on youtube claim all Dutch drivers are taught this but that's not true. I've never seen someone use that technique.
In the Netherlands the risk of using a bicycle is probably vastly lower than elsewhere. All cars are used to bicycles being everywhere. Most drivers probably use bicycles, too. There are tons of bike lanes that are physically separate from car lanes. Etc. So one could argue that the risk of a severe injury from riding a bicycle is so low that you feel it's ok not to wear a helmet. Clearly most dutch people think this way.