I do not know if it was mentioned in the article as I did not read it fully, I'm Finnish and am sort of tired of reading or hearing about this particular subject, but it is worth mentioning that all Finnish teachers are required to have a Master's degree to qualify as teachers (even kindergarten ones). Since higher education is free (there are no private universities in Finland), the threshold to study to become a teacher is very small, and usually there is quite a surplus of teachers in popular fields, in hard sciences as an example.

Those that select a teaching curriculum in the university spend 1-2 years interning in schools during their studies. Most people end up taking up teaching curricula just because it is a sure way of getting employment especially if one is studying a field in which employment is scarce outside of academia, say, philosophy.

I myself am studying computer science and I plan to enroll in a teaching curriculum should life in academia turn out to be boring, mostly because a) teaching is fun b) it pays relatively well c) a three month paid vacation from June to the end of August is a plus and d) it is a respected profession.