In 1970 minimum wage was $1.60/hour, equating to about $3.3k a year. A typical mortgage was about $126/month. Car payment, around $100. You weren't raising a family and saving on minimum. Median income was about 3x that for a family, so you could definitely raise a family and save at the median. Note, these come from querying AI, but they match my recollections as a child a few years later.

Today, family income is up about 10x, but costs have risen much more than that.

In my opinion the two greatest factors on the reason, in the US at least, for the changes, and not having children were - birth control became widely available in the US in the early 70s, and women entered the workforce in great numbers. This greatly increased the amount of family income, but costs quickly rose to basically eat up all the extra income.