Why does the Netherlands have such a strong biking culture? Most of the country is flat, the cities are compact (at least by Chicago standards) and the weather never gets too hot or too cold to bike. One can reliably commute by bike nearly every day of the year. The country has many dedicated bike paths and marked bike lanes on many major roads. Traffic laws greatly favor bikes over cars. This all gives positive reinforcement to bicycling in this country.
Bicycles here for the most part do not have hand brakes or multiple gears but are otherwise rather sturdy. Bicycle lights are required at night; a visiting complexity theorist got a ticket for not using his. Virtually no one wears a helmet. When we lived here on sabbatical we would put our one-year old daughter on a bike seat on the handlebars without a helmet—the norm for Holland but might have gotten us arrested back in the states.
Bicycle theft is a big problem especially in the cities. The general rule is to spend as much on the lock as you did on the bike. Locking up your bike requires knowing your topology; Get it wrong and you might lose a wheel or worse yet keep your wheel and lose the rest of the bike.
Most people in Holland don't bike for health or environmental reasons. Bicycling is often simply the easiest way to get from point A to point B.