A bicycle also typically is much less fast than a car, so when you fall, the damage is also much less bad.

As someone who have seen someone fall at walking speed without any outside influence and end with a basal skull fracture, I call bullshit.

There’s a huge difference between falling and falling because a car drove you over.

Yes, there is. I am however not advocating for wearing heavy proctive gear that would make a difference in such a case, but for helmets. And hitting your unprotected head can simply heavily injure or even kill you -no matter the circumstances or speed- just by hitting an edge, a curb, a random pebble or just aspllated ground at a bad angle.

If basic anatomy would allow for humans to fall over and hit their heads while standing or walking around normally, we would already be wearing helmets all the time, just like we are causally protecting our feet with shoes.