Google "productivity vs labor graph". In the US at least, the "tremendous labor to be done" is a lie that keeps grows each and every year.
To me this alone would explain the flatness. I sense some sarcasm in your comment - maybe it doesn’t to you.
That wasn't my intention.
Do you mind giving me a link to the essay?
I couldn't find the essay on the web, but it's in the book https://www.amazon.com/Praise-Idleness-Other-Essays/dp/00430... which is well worth reading.