A broader explanation would be that contemporary America is a society that, in a variety of ways, doesn’t take very good care of its children. Recently, Unicef issued a report comparing a number of measures of child well-being in 21 rich countries, including health and safety, family and peer relationships and such things as whether children eat fruit and are physically active. The report put the Netherlands at the top; sure enough, the Dutch are now the world’s tallest people, almost 3 inches taller, on average, than non-Hispanic American whites. The U.S. ended up in 20th place, below Poland, Portugal and Hungary, but ahead of Britain.
Well, according to my understanding, based on conversation with a Dutch person, in the Netherlands there is strong social pressure not to be short and consequently there is use of Human Growth Hormone on children who would have been quite short without it. So I would rather have been told not about the Netherlands but about the #2 country, and to be given some criticisms of the Unicef criteria.
This is just a wild guess inspired by animosity towards paste manufacturers, but I’m going to guess that Americans used to be taller than Europeans largely because they ate better bread than Europeans did, but in the middle of the 20th century, at all socio-economic levels, Americans, but not Europeans, switched to eating a vaguely bread-like paste useful only as a cleaning compound, although I haven’t had much success with it even for that.