Day Trips around Amsterdam... but why a bike ?

Those Dutch and their bikes. Two of a kind ...
Yes, the country is pretty flat. Yes, it's a small country of short distances.
But that doesn't explain fully why, yes indeed, the bicycle IS ideal to visit this country.

Two very crucial reasons : infrastructure and social acceptance.
So, just a bit of history. Or what else did you expect on a site like this ?
If you're not interested in historical explanations, stop reading, and just believe me when I say that a bike is perfectly handy for these small country roads, bike paths through woods and wetlands, in historical cities with narrow streets, and that you don't have parking problems.
If you want to hear more, read on.

Bicycles became practical and reasonably affordable a hundred or so years ago. Interesting to see how very differently things evolved in two neighbouring countries : the Netherlands and Germany, where at least the northern part is equally rather flat.
In Germany the bike became very popular in circles of workers/unions/proletarians ; higher classes (and would be's) kind of turned up their nose at the bike, they had their fancy real horses. And then came the First World War, and all the Germans surely had other things on their mind.
More or less the same starting situation in Holland, but this country remained neutral in the first war, and in peace. And for workers and middle class alike, the bicycle became an accepted reliable and solid means of transport. Perfectly fitting with how the Dutch liked to see themselves : a sober hardworking people, where showing off was not appreciated, an island of reason in a world sunk into total madness.
As there was a social and political consensus on the place and meaning of the bicycle, the state began developing an infrastructure for this new vehicle. Gradually an impressive network of (separate) bicycle paths, road crossings, signposts, bridges, etc was created. Other relatively simple measures favoured the use of a bike, like e.g. the obligation for every new built house to have a shed of some kind for bikes. Even flats had (and still must have) their own "basement box" where one can put the bike(s).

Of course, also in the Netherlands, the car became dominantly important since the 1960-ies.
Still, then as today, all children in this country grow up with a bike. Meaning that every car driver knows from own experience that it is a very unpleasant feeling when a car races past you closely. That makes a difference.
You have fools everywhere, but generally car drivers behave reasonably towards cyclists. The more, if they know what your intentions are, so make that always clear, and in time !
The same in the Netherlands as in other countries : the last 20 years or so the bicycle acquired an extra environment-friendly image, and the sporting aspect gained in importance. But the big difference is that over here, the bicycle is and always was primarily a generally accepted vehicle to go from A to B. Nothing more, nothing less.
You can't say that of many countries.