In an intact two-parent family that is how it is set up by the traditional division of labor. In a single parent family, as ND explained quite comprehensively, full maternal custody after divorce is a relatively recent development in our society. We now have an entire adult generation of adults raised under this matertnal custody system - this segment represents 80% of those incarcerated in our prison systems nationally. Meanwhile, the children of custodial fathers have an incarceration rate lower than those coming from two parent families. While we cannot establish cause and effect, we can unequivocally declare that the system is broke. By all appearances, it's been broken intentionally and nobody intends to fix it from the inside.