Life is fragile. Especially on a bike. I once survived getting hit at 30mph and I can't even remember all of the stories I was told about how lucky I was.
I probably heard about a dozen different ways children of friends (I'm Dutch) died from just being hit at 5mph and hitting their head the wrong way when falling.
It's indeed not mandatory. Biking in general is still much safer than in the US though since we have a strong biking culture, good infrastructure (separate bike lanes and traffic lights) and laws that (nearly) always hold the car responsible for any damages.
I probably heard about a dozen different ways children of friends (I'm Dutch) died from just being hit at 5mph and hitting their head the wrong way when falling.