If that comparison was apt, we wouldn't see so many people out riding sans protection. But we do, and it's because they have a share bike that didn't come with

If that comparison was apt, we wouldn't see so many people out riding sans protection. But we do, and it's because they have a share bike that didn't come with a helmet, or they were worried about messing up their hair, or they lost their helmet, or they left it at the destination, or they're a rebellious teenager who just doesn't care, or no-one educated them about the risks, or they just forgot to put it on. A better comparison would be to flossing your teeth, or wearing sunscreen: everyone should do it, but not everyone will do it.