Technically, most bike accidents take place at low speeds without the head ever striking the ground. And the small fraction of such accidents where the head does strike the ground result in no significant injury. So what you are really saying is that a helmet is good at protecting from insignificant injuries in a miniscule fraction of bicycle accidents.

Which is true so far as it goes, but makes one wonder why you spend so much time ranting and whining about people who aren't concerned enough about the prevention of unlikely and insignificant injuries to do exactly what you think they should.