There is ~250 cycling related traffic deaths per year in the Netherlands. Some 60 of those are e-bike related.
Normalized per capita that is well above the EU average, but you shouldn't forget that we cycle a lot in the Netherlands, which means that per cycled kilometer, cycling in the Netherlands is still ridiculously safe even without helmets. It has been argued that forcing people to wear a helmet in law will reduce trips taken by bicycle and increase air pollution due to an increased number of trips taken by car (25% of ALL trips in NL are taken by bicycle, versus about 16% in Denmark, to give some comparison). And this is not even counting the psychological effect it has on car drivers and their behavior around people wearing helmets. Besides: cycling injuries and deaths are skewed heavily towards the elderly population (65+), if you're a 20-something person, statistically speaking you're more than fine not wearing a helmet in the Netherlands.
Let's not jump to conclusions here about helmets and think this stuff through before shouting 'You should wear a helmet'. It's not quite that black and white. Forcing everybody to wear helmets might very well cause more death and injury than not to. We have taken other precautions to ensure cyclist safety, such as designing our roads to protect them, and those measures make a lot more sense. You shouldn't forget that a helmet only helps a little if you are already in a bad situation (e.g. an accident), so it's much better to prevent that situation from occuring in the first place. The Youtube-channel Not Just Bikes has great explanations about how we approach those problems over here.