Don't discount that some people struggle with the object of parenthood more than others. Maybe they'd led a more selfish life, weren't brought up to be yielding, giving, or responsible to others, and their journey required more growth than they'd anticipated.
If they didn't know that they weren't prepared, how could anyone else?
As a younger man, I spent longer than most parents actively raise their children caring for elderly family. A minor difference to child rearing is that when you no longer need you to help your children or change their diapers, it's generally not because they've died.