I can't speak for everybody, the following is just my personal opinion as to why I like Dutch bikes....
I am a big fan of Dutch Bikes because well.. I am Dutch and I have had them all my life..
I particularly like '' Amsterdam Bikes'' as its my home town and because of their craftsmanship and attention to detail ....not to mention nostalgia from my childhood...
looking into the window of the RIH and Presto shop on my street..
In the Seventies you would go into one of the shops, RIH, Zieleman, Presto, etc, meet the builder himself, get measured on a bike sizing jig and off they went and build you a fantastic frame!!!
They would also discuss the paintwork, components etc....a great experience overall..at a price though..
As you say they are very clean rides, and in my opinion their characteristics are; very fast, sturdy and beautifully crafted!!!