"back then" a family could live on a single income.

This was largely for relatively privileged people. Most families the mother worked as a teacher, nurse, domestic, secretary, nanny, etc.

Common misconception. Poverty levels were far higher. In 1950 half the global population lived in abject poverty. Today, it's less than 10%.

https://ourworldindata.org/poverty

They had to. Outside a few vocations, women weren’t allowed to work.

And now they have to work because a single income is no longer enough. Yay for progress.

Some people could. There was also a lot more abject poverty.

Working a minimum wage could buy a starter home "back then". It now can hardly pay rent, and starter homes essentially no longer exist, even if someone wanted one.