

You are comparing apples to oranges.
A high-visibility vest does not protect you at all. Its only purpose is to make drivers pay more attention to you instead of actually protecting you.
A helmet actually protects you. Also not just from some specific danger that shouldn’t be there in the first place (cars) but from the results of every possible fall no matter what caused it.

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