Having kids outside marriage is frowned upon in general in any civilization, and marriage correlates strongly with having children. Also a contemptuous view of "housewife" shows a disregard for how demanding motherhood is (or fatherhood is, for that matter). This is a worldwide problem, save maybe for Africa, something we also see in the liberal West. People have just become comfortable and hedonistic. Having children is not comfortable. It is demanding. It requires thinking of someone other than yourself (as does marriage, also affected by this mentality). Given the choice between a nicer house and another child, many today in the West would choose the house. Consumerism, hedonistic views of sex, keeping up with the Joneses, all these contribute to reduced birth rates. Japan is clearly about as demoralized as the West, whatever the precise causes.