School demographics matter a lot. The Harvard crowd isn't finding their future wife at school.

Huh that surprises me. I would have thought that's exactly the kind of middle-class crowd that'd want to marry-in?

Once you’re in that crowd you continue to run with that crowd- there is no hurry to get hitched at that age, the opportunities to find a match after you’re established professionally will still be there.

Harvard graduates are going to have multiple partners before settling up and marrying by their mid-thirties