Because in the US, those are the only cities that have the public services to make them a truly cohesive unit: in Phoenix, for instance, the houses are too wide

Because in the US, those are the only cities that have the public services to make them a truly cohesive unit: in Phoenix, for instance, the houses are too widespread, and the downtown too filled with parking lots, to allow for a strong sense of the community as a city existing (I grew up just outside Phoenix, and if you don't have a car, i.e. are 14, you can't engage in city activities, such as the zoo, or museums, etc.. And even when you do have a car, it doesn't feel like a city when getting from a typical home to a D-Backs game takes 45 minutes, and then you have to walk 30 minutes to get from the parking lot, and while you're walking you only pass industrial lots and parking structures).