I've seen people run to strangers aid in the biggest cities on earth. Perhaps "aloofness" is just more acceptable to some.

In my experience in London, the people living in the centre are not aloof, but it's the commuters who switch off their brains on the train or in the car and forget to switch it back on when they're in town. But that's an extremely broad brush, so don't take the categorization to heart.

In DC the natives are plenty friendly. It’s the suburban transplants who moved here from elsewhere who tend to be wrapped up in themselves.

I found this wasn't universal. Grew up in relatively unfriendly (especially for a Canadian city) Toronto and then moved to Chicago, found people were much more outgoing and friendly in the midwest, even in the city. In the bay area now and it seems like spending too much time driving with other angry drivers (from themselves spending too much time driving) makes everyone irritable.