"When it comes to choosing a mate, height tends to have (only) a small effect, which is not very surprising given the many other, more important, traits people value in their mate."

I think this may be wrong. Most all women I've ever spoken to have a preference for a taller mate than themselves. Which would very well mesh with their other finding:
in the United States, shorter women and men of average height have the most reproductive success.

Its also a question of mobility and population distribution. In the Netherlands the population is concentrated in very few centers and even those living in the countryside have easy access to cities (i.e. to a 'large breeding pool'). In the US that is not the case. So I find it not surprising that the development would be more extreme in a small country than a large one.

@antialias

I have also not seen a more homogenous population in all of my traveling. Their plainness makes white bread look exotic. This makes me think that the narrowness of the aforementioned 'pool' is reinforced by a preferential selection for very-like mates; whereas many other heterogeneous populations like the US limit the bottlenecking/spiking of particular traits.