I've noticed similar in some European cities in terms of an apparent higher average density. I've always attributed it to cities that have existed longer, and that were already significantly more established by the time technology (bicycles, trains, cars) helped people commute further.

In the absence of this technology, I've always assumed people tended to stay more local, which meant that cities ended up a cluster of local communities, rather than one large central district with a large number of commuters.

That said, this seems to conflict with the example of Tokyo, which I understand was significantly rebuilt after the second world war.