Running 10k a day is definitely not the norm, most people don't even walk 10k a day.
Even then, sitting 8h a day in front of a computer is a quite modern plague and the root cause of most "back pain" issues (an insanely prevalent issue, even just counting medically reported cases) because of core atrophy.
For people who do run, which is quite frequent hobby, 10km is not all that much. My point is, quite a lot of educated people or middle class people do sport frequently and regularly. The back pain you mention is sometimes the trigger for it.
Whether it is running, going to the gym, calisthenics, yoga, or swimming, the richer "mollycoddled" and supposed "Karens" op mockingly referenced as spoiled are specifically the people who do sport the most.
I think the point is that if you don't walk 10k per day it doesn't make you "civilized". It just makes you a person who doesn't walk 10k per day. No judgement required
Even then, sitting 8h a day in front of a computer is a quite modern plague and the root cause of most "back pain" issues (an insanely prevalent issue, even just counting medically reported cases) because of core atrophy.