I acknowledge that this article is aimed at Americans, but I don't really think that bilingualism is rare in the world, or for that matter, in certain parts of the USA.
Perhaps this is not relevant to the article, but it seems that bilingualism is a forgotten issue these days in the USA. Yet, it is actually a very important issue. One time a person simply told me that they couldn't see the point in Junot Díaz work because it used so many 'foreign' words.
At the time of writing this reply, there were already plenty of other replies that suggested that we should all speak English exclusively or at least that speaking English proficiently should be prioritized. I think that they are probably at least partially right, but it surprises me that there is really not a lot of controversy on this topic.
All I am saying is that here we have a perfect topic in which humans are not entirely rational, and instead of being puzzled and talking about it, we just simply forget about it.
[edited for clarity. Like Celia said, my English is not very good looking, so I'd appreciate corrections :D]