And I've seen the same in the USA, and other places.
It's a big city versus small town thing. In the remote wilderness everyone helps each other. In the city it's assumed you are gong to get help from someone else.
I've seen injuries in public in other countries big cities too, and I've just kept moving because someone else is helping. The way people act in China is something else.
Giving any consideration to strangers doesn't even cross their minds and it shows in all kinds of little ways: refusal to yield any space, be it a lane on the road or part of an aisle in a store, public spitting, urination, and yes, defecation, refusal to queue or allow people to exit trains, elevators, or other vehicles before pushing in. Also, strangely, it's not the young punk kids annoying their neighbours with their load music, it's hordes of middle aged dancing aunties.
It's a big city versus small town thing. In the remote wilderness everyone helps each other. In the city it's assumed you are gong to get help from someone else.