Graphs like these serve to suggest to people that there's a single, operative reason at their core instead of it being a complex, multivariate issue.

They also tend to cause people to over-attribute the effects of the story told in the graph(s) to the majority of the population instead of a minority with disproportionate impact.

Regardless, taken together the graphs are compelling. The real cause will likely remain forever elusive, but here's a few hypotheses. * The rise of globalisation and the outsourcing of low skilled jobs to other countries. * The abandonment of the gold standard. * The oil crisis. * The disarmament of labor union power. * The concentration of a highly educated 'creative class' in fewer urban areas. * Women entering the work force en masse.