Why Holland?
I agree with the points about a. strong winds and b. lifestyle incorporates cycling more.
The lifestyle/culture of cycling might be the most influential. If the weather turns good in spring you can see tens of thousands of cyclists cycling recreationally outside of the towns.
Some own observation and stories from Dutch friends.
1. A Dutch Secondary or Grammar school can have a large percentage of pupils cycling in from the same city and outskirts, but also from surrounding villages (up to 5 miles is not too out of the ordinary).
2. Many Dutch school-kids will cycle to school, friends-visits, sports, dancing, and other pastimes. I recently read that the average family with teenage kids drives 2100 miles a year for the kids runs.
3. Many university students will have the bicycle as their main form of transport. I'm ot sure about average mileages etc. but someone who leaves university will have done a fair bit of cycling up to that point in his / her life.
4. I know a photographer who lives in Amsterdam and who recently bought one eBakfiets (carrier bike) aside from his car. Most of his shoots are in Amsterdam and he said he often got stuck in traffic in a car and averaged 4 to 8 parking tickets a month to be on time (at 65 to 130 euro each). With the electric bakfiets he was usually on time and could carry all his stuff. Point is: Many inner cities are hardly accessible by car, the nice historic centres with canals have many small streets that can easily be blocked by cars that are parked the wrong way, utility vehicles etc.. Parking is often even harder.
5. I had a Dutch friend visiting and I asked him after a couple of days what he thought were the differences between the cyclists here and in the Netherlands (aside from there being less of them). He answered: a. There are mainly mountainbike style bikes here and in Holland there are more bikes for riding on roads, less rolling resistance. b. Most cyclists here have no mudguards and you can see marks of muddy water on their backs and backpacks, in Dutch cities we always say "the one riding without mudguards is the one trying to wipe the dog-doody out of his neck and hair". Mudguards are the norm in the Netherlands. I spoke to him recently. He himself has recently bought an ebike for his daily 10 mile commute (5 in 5 out) which he did for years without electronic support. He works on several innercity locations and has to go to meetings.. He said that commuting on the bike was brilliant, but he was concerned about the bike getting stolen with him moving around town a lot. He said he was considering getting a cheap second-hand bike for getting around the city centre.
I am not sure to what extent Dutch people will be getting electric bikes, but with the roads and cities cluttering up it may be a more and more realistic alternative for many.
Just my 2c.
btw. these 2 pdf's have much info on numbers of bikes, kilometres ridden and so on and so forth.
Cycling in the Netherlands - Fietsberaad
Facts about cycling in the Netherlands - Fietsberaad