BEN5, to answer your post: 40 years ago.... hmmm, that was when I was little.
a) Mortgages were relatively far cheaper than these days. eg We lived in a fairly standard 3 bed home. My parents were able to borrow the mortgage money on the basis of one income, and make the repayments on one income. Yes, money was pretty tight, but it was all perfectlty possible.
b) A lot of other essential bills were either non-existent, or relatively cheaper. eg Council tax, utilities
c) Women of that generation often hadn't had access to the same opportunities as now. Girls achieved less well at school in many subjects, far fewer girls than boys had gone on to further or Higher Education. My mum, for example, was as clever as my dad, but she had been pushed to leave school at 16, whereas he had been to University. This meant that many women never had access to the higher status, more interesting careers in the first place.
d) The cultural norms were very different 40 years ago. As a young child, very few mums that I knew continued working. The expectation for many women was that work was something that you did for a few years between leaving school and getting married and having children. Average age of marriage and first child were quite a lot younger than nowadays. Some women returned to (generally) low status 'pin money' jobs when their children were older, but many continued to stay home. This fact was reflected in the almost total lack of childcare facilities then. I didn't have any friends who went to a childminder, and after school and holiday clubs were pretty much unheard of.
BTW, playing outside on bikes, going for walks, are things that many parents enjoy, whether they stay home or not. Also, as parents, we all invest in the future with our children.