You've turned logic on it's head. We live the vast majority of our lives not wearing helmets. That includes many activities where there's a real risk of head injury, maybe greater ot less than when riding a bicycle.

So the logical question isn't why not wear a helmet, it's why wear one.

Your simple answer is that it's dangerous to ride without one, which is an opinion you're entitled to. But others may not feel the level of risk is high enough, and therefore don't . It's that simple, it's not about helmets, it's about the rik of head injury and how to manage it.

The risk assessment issue represents a spectrum, and some may feel that it's too risky to ride a bicycle without a helmet, others may feel that it's too risky altogether and not ride at all, especially on public roads.