My reading of the article is that it happened, as they say, "slowly and then all at once."

Not dissimilar from the hollowing out of rural America today. People keep on going, assuming that things will either stay stable or turn around at some point. Meanwhile everything keeps on at roughly the same trajectory of the people hanging on getting older and older, and the young people moving on to greener pastures.

And then one day you realize that there isn't really anything left.