In the post war boom, most of those entry level jobs that could support an entire family were limited to white (itself a heavily restricted term back then) men with a union membership.
Heck, unions themselves were heavily racialized back then.
On top of that, housing was segregated either overtly via race restrictions or covertly by overwhelmingly denying loans or sellers colluding to not sell to "that" family.
You'll hear plenty of these stories from older Black, Italian, Greek, Armenian, Chinese, and Hispanic Americans.
That’s true enough, but at that time whites were 90% of the US population, so there was arguably enough wealth then, definitely enough wealth these days, to extend entry-level jobs to the remaining 10%. When 40% or more of your population is descended from post-1965 immigrants, the competition for good jobs goes up a lot in most industries, unless enough economic growth makes up for it - and even with growth, housing scarcity is almost always an issue.
Wages from a single entry level job absolutely did not support a family of 4 or more in the 1950s and 1960s, let alone as comfortably as you are probably imagining.
These delusions need to stop, because it makes it impossible to have meaningful conversations about the many actual issues that do exist. I would expect people here to be better informed, but that seems to be less and less true over the last couple years.
And yes, the wealth distribution is more uneven now than it was in those days, but not to the point that you are claiming.
In the post war boom it definitely used to produce enough value to support several people.
And we're far wealthier in aggregate now than before, it's just distributed badly now.