I don't think it's really a question of "enjoy your riches," because no matter what your status, nobody can "afford" children, not even the ultra high net worth individuals. It's a burden regardless.
But I think therein lies the answer. There was a time not all that long ago that not having children was a burden. Who was going to bring in the harvest, or at the very least supervise bringing in the harvest? Who could you really trust to take care of you properly when you got old? And of course, there's a biological compulsion as well, but that's much easier to sidestep only in the last couple generations.