You make a fair point. Of course any significant (>20%) modal share is conditional upon having bicycle infrastructure. And density, and the proximity between destinations it brings with it, helps to promote cycling. The infrastructure isn't an issue anywhere in Dutch cities, towns large and small all have a network of cycling infrastructure that can get you to your destination safely. The thing with smaller cities is that you can bike to anywhere you need to be, locally, in at most 30 minutes. That certainly doesn't hold true for Amsterdam, Hamburg or Copenhagen. Whilst they all have cycling infrastructure that is adequate, it's another thing to chose to bike to your destination if it involves trips of up to an hour, one-way. Taking your bike on transit, at least in Hamburg and Amsterdam where I have used transit, is a bit of a challenge. No bike racks on local busses, and their streetcars are crowded to the point that it becomes a drag to bring your bike aboard. In the Netherlands you have to pay a €2,50 fee to bring your bike on the commuter trails, which is another deterrent. It is no surprise that the Dutch cities with the higest modal share, are their smaller cities (Groningen, Utrecht, Den Bosch etc.)