these same places motorcycle without helmets too.

it doesn't make it a wise choice.

I mean, wearing a helmet is still the smarter thing to do. I don't, because I don't go very fast anyway and wearing one feels quite uncomfortable, but it's still always the safer choice.

That said, the actual benefit is vastly reduced if

1. you just go at relaxed speeds
2. car drivera are very aware of cyclists existing and as such drive more carefully
3. good bicycle infrastructure means there are few points of contact with larger vehicles anyway

Since helmets only matter in severe accidents, if your odds of one are very low in the first place, they don't change too much. But you can of course always get unlucky. Just like you can get unlucky with a helmet and ram yourself shoulder first into a tree and break your spine.

In a car, the belt prevents the body from sloshing around in the car.

With a belt, wearing a helmet would increase the inertia of the head in a sudden deceleration.

I can take pictures like this in heavily car trafficked areas as well. That still doesn't mean they're safe, or sane.