Why are there many people cycling in the Netherlands?

because it's cheap, silent, odorless, fast, uses routes not offered by public transport... and doesn't require nearly as much parking-space a a car would.

You are aware that the Netherlands has a population density of over 400 per km² aka over 1000 per square mile, right?

In other countries roads are setup wide and long, suitable for cars and mass transportation. People there have their own carport and on their way only small number of obstacles like traffic lights. Towns and villages are older in The Netherlands.

Take in consideration that Dutch love to pay tax and that shows! Many things are well organised. Having a car and prices of fuel and paying road tax are all too far to reach for the average. I am having a motorcycle for getting out of town and like train travel because of the coupons: Euro 20 for a day when you know up ahead. My millage on bike is about 10 a day but 20 or 30 is no exception. Our town has traffic circulation, that means you can not go from one part into another. Crossings often have surface uplift because the European Union subsidy for safety and one often has to pay for parking. See you at the gas station or at the shop for repairs, then you'll see who is fast.

Because it's easier there, the infrastructure is set up for it.

dont have money for fuel

The land is mostly very flat and the weather is ok for cycling in the majority of the time.

The topography suits cycling.

Because much of it is flat.

Because distances are short, the climate is reasonable, and my own city becomes difficult to reach by car during rush hour.