[myrmidon]

My point is: Society itself recoups the investment into education very easily (from competent taxpaying workers some years later), but the main cost of raising children is paid by parents, and they don't get back anything (economically).

All the benefits that used to be there (adolescents helping with farm/work, children taking care of aging parents) became more and more irrelevant, but general costs of raising children (to parents) have not decreased at all (and "reputational" cost of just skipping parenthood is at rock bottom, too, so that is no longer pushing prospective parents towards economically irrational decisions, either).