In The Netherlands, virtually nobody wears a helmet. Keep in mind nearly all cyclists are on the way to something, not using it for fun: 99% are on the way to work, school, shopping, or whatever most Americans use cars for. Therefore most people wear whatever dress they wear – nobody wears a helmet. And the number of cyclists dying davka from traumatic brain injuries isn’t all that high, I believe – in fact the number of cyclists getting killed on the roads is quite low.
The critical difference, as some mentioned above, is that in other countries, car drivers are rude and do not respect cyclists. In The Netherlands cyclists are considered full participants in traffic, plus, there are separate cycle lanes near all major roads, inside and outside of cities.
I think that’s what the problem is; I experienced it in Israel, where the attitude to cyclists seems to be similar to the US. Cyclists are considered an annoyance, just jokers fooling around and bothering the innocent poor car drivers who need to get to work, so it seems. In Israel, cyclists have no rights at all. In my first few months in Israel I had a bicycle; when I moved from Bnei Brak to Yerushalayim I sold it since I felt it was way too dangerous there as well, plus the hills make it impractical. (I sold it to someone who wouldn’t use it in Yerushalaim either, by the way – no lifnei iver).
Here in the UK, there is maybe 3% the amount of cyclists one sees in The Netherlands, which is still 10x more than in Israel. But here all of them, including the ones going to work, *all* seem to wear helmets and hi-vis vests. And many of them wear not 2 lights, but 4 lights – like, regular bicyle lights and helmet lights, and even have them on during the day. Recently I saw a cyclist with a front light *brighter* than that of the cars passing him!
I think somewhere in between the UK and Netherlands would be best.