Another difference (in addition to the other responses) is that thirty years ago, DINKYs bought houses at prices that a single-income family could afford, then

Another difference (in addition to the other responses) is that thirty years ago, DINKYs bought houses at prices that a single-income family could afford, then sold them on (or let them out) at prices only DINKYs could afford. A middle-class two-income late-20s couple 30 years ago could still comfortably afford the mortgage or rent on a family home if the lower earner stopped working (as was almost always the case when a baby arrived).