"(Before you ask why he didn't just move to find a job: he couldn't leave the area because his ex-wife was still alive and he couldn't move the girls more than an hour from their mother, so he was pretty much stuck.) "To the extent we have increased the number of children living in one-parent households over the years, we may have increased the obstacles to moving for jobs. Similarly, the number of two-job households would also increase the obstacles. For example, in the most extreme case a two-professor marriage needs complex negotiations with a new school in order to obtain new jobs for both.
Net result, the decline in mobility noted here.(Tabarrok at Marginal Revolution says it's land use restrictions.)