In the old economy, aggregate demand collapsed for some reason, and workers got laid off, then called back to work when orders recovered. These days, it is more likely that your job and industry has gone away entirely. That has particular implications for a skilled economy. In 1930s, when FDR was trying to combat mass long-term unemployment, all he needed to do was create a construction project; most of the men in the country did some sort of hard physical labor. It was relatively easy to create jobs that they could fill. But what kind of public works projects would absorb mortgage brokers or mid-level managers? As jobs have gotten more skilled, more human capital is specific to firms, industry, and job classifications.
The quoted article and comments contain a lot of good information and a variety of interpretations. It’s all about three levels deeper than what you’ll encounter in the popular media.