The more crowded a place and the higher the population, the more formal the culture and the more you need mechanisms to protect your privacy and politely but effectively tell a zillion strangers to butt out.
The human mind is designed to work with a "tribe" of about 150 people. Above that and we have to layer culture and learned behaviors on top of innate traits to make the whole thing not implode.
I used to think this until I spent some time bouncing around East Asia. Tokyo is not even that dense relative to other high functioning Asian mega cities. Seoul is 3x, Taipei is 1.5x. They're much less polite places than Tokyo and manage to function really well.
The human mind is designed to work with a "tribe" of about 150 people. Above that and we have to layer culture and learned behaviors on top of innate traits to make the whole thing not implode.