The parsimonious reason is that people write songs about comfort and large, happy families, not about AGIs and statistical households of 3.3 to 3.7 people with 1 to 1.44 breadwinners. Songs (and media) reflect cultural values, not cultural realities; see also rosy movies about the "good old days" of 1960s USA being not particularly representative of the period's racial and economic strife.