To clarify my question, I think that Bloom is describing a true social phenomenon. It's the "why" behind his "what" that I'm not sure about. Are men really that indifferent to children and family? Is the abstract desire to have "a family" and children an exclusively female desire? Is it really true that in ages past a lifetime of commitment could be purchased on the strength of charms and wiles alone?
Locke believed, and the events of our time seem to confirm his belief, that women have an instinctive attachment to children that cannot be explained as self-interest or calculation. The attachment of mother and child is perhaps the only undeniable natural social bond. It is not always effective, and it can, with effort, be suppressed, but it is always a force. And this is what we see today. But what about the father? Maybe he loves imagining his own eternity through the generations stemming from him. But this is only an act of imagination, one that can be attenuated by other concerns and calculations, as well as by his losing faith in the continuation of his name for very long in the shifting conditions of democracy. Of necessity, therefore, it was understood to be the woman's job to get and hold the man by her charms and wiles because, by nature, nothing else would induce him to give up his freedom in favor of the heavy duties of family. But women no longer wish to do this, and they, with justice, consider it unfair according to the principles governing us. So the cement that bound the family together crumbled. It is not the children who break away; it is the parents who abandon them. Women are no longer willing to make unconditional and perpetual commitments on unequal terms, and, no matter what they hope, nothing can effectively make most men share equally the responsibilities of childbearing and child-rearing. The divorce rate is only the most striking symptom of this breakdown.
-- Allan Bloom, The Closing of the American Mind (Simon & Schuster, 1987), "Relationships," p. 115