It is difficult to afford raising more than two children on your own as a married couple. You have to enlist outside help. If you don't have a family to fall back on you have to purchase help. At some point one of the married couple needs to stop working instead of paying for childcare as the cost of childcare will exceed the income of one of the partners. Both partners want to maintain careers in the western world which applies further strain to the arrangement. I would have ten children if I had affordable childcare and additional help around the house. It is clear to me.