Alternate hypothesis: population mobility is caused by fewer career opportunities overall and clustering of what opportunities exist in urban areas. Move or starve.
That really doesn't contradict what the person you're replying to said. Your comment manages to be both jerky and irrelevant. It ignores the principle dilemma, which is that taking care of children is easier with a broad family support network, and if you don't happen to have one of those near where your job is located it is harder to take care of children.
Parent didn't try to contradict the grant parent, nor they tried to address their "principle dilemma" (sic).
They merely provided an alternate hypothesis on the root cause of population mobility: not an overall increase of career opportunities attracting people away from their hometown, but a scarcity of career opportunities, where mostly jobs clustered in larger cities remain.
Maybe refrain calling other comments "jerky and irrelevant" when you've missed their point, and don't even understand their aim?