https://en.wikipedia.org/wiki/List_of_cities_proper_by_popul...
https://en.wikipedia.org/wiki/List_of_cities_proper_by_popul...
In the 50es through 70es, there was a strong need for extra housing which led to the projects outside Paris ("citées"), to many factories torn down to make space, but also to much higher residential buildings here and there. Still worked fine (well, not many of the citées worked fine).
And people really, but REALLY love being able to walk to their preferred local baker and pastry shop (out of a choice of several of course), and to the local grocery store. The density has to be high enough to support these.
Turns out, high density also allows a great subway system. Nobody complains that it exists.
The other is that while the buildings are certainly tall, China also does a lot of "tower-in-the-park" style development where the plazas and landscaping in between tall buildings decrease overall density.
This will spell economic worries someway down the road as maintenance upkeep costs start to kick in.