"An economic mystery: Why do the poor seem to have more free time than the rich?"
By and large, the biggest leisure gains have gone precisely to those with the most stagnant incomes—that is, the least skilled and the least educated. And conversely, the smallest leisure gains have been concentrated among the most educated, the same group that's had the biggest gains in income.
Ok, I'll take a stab. How many of these poor are actually working? Maybe they have so much more leisure time because they don't have a job.