And that support was a family of 4-6 in a 1200 sq ft house, eating out <6x a year, vacations were picnics at the local beach, one car that you did your own maintenance on, one tv, only one set of good clothes (your Sunday outfit), et cetera. Most places in the US can still support a family at that same level of expenditure on an average income.
The difference is the social structures supporting that kind of life have disappeared.
That exact same 1200 sq ft house is now 300k in the Midwest, if it's even for sale at all, and it's likely a rental for $2.5k/month.
In many cases it's illegal or commercially unviable to build said 1200 sqft house.
It's kinda funny that this is considered small, though. 110-120 sqm is perfectly normal for a family of 4 where I live, and in many cases they do it with 1 or 0 cars. But I live somewhere that isn't horribly designed (the Netherlands)