You’re 100% correct, there’s plenty of hard unmoving objects that necessitate ski helmets. When I was in my 20’s I hit an ice patch while skiing and went into a tree sideways, hitting so hard I almost severed my quadriceps without breaking the skin. A ski patrol saw the incident and assumed my leg was broken, they were dumbfounded when I stood up, waved them off and skiied away. It wasn’t until the next day when I got out of bed and face-planted that I realized how bad it was. Was on crutches for over a year. Helmets, kids.