If they are perfectly happy and satisfied with their decisions and can live wiht themselves...who are we to judge? Some people still feel that a divorce has traumatic effect on children, so if the man IS treating the family well, it's her choice to stay. Also, not every woman is an "independant woman" who can support herself (not just talking financially), so she doesnt want to leave. And if certain conditions are met, they will prefer a comfortable life over the life of a financially struggling single mother... .
you brought up a very good point....I can see why some may put up with it.