And conversely, the smallest leisure gains have been concentrated among the most educated, the same group that's had the biggest gains in income.
That one's easy. There are two factors at work. First, the number of people willing (and perhaps able) to invest the time & effort needed to become highly educated & skilled is smaller than the demand for people with those skills. (Which is why we have H1b visas in the tech industry.) So these people and their employers have incentives for them to work more hours.
Second, these people are, by and large, interested and involved in their work. If they (or perhaps I should say we, since I'm one of them) have to spend more hours staring at a screen, they'd rather put in the extra hours coding than watching TV programs intended for the brain dead.