It could be also the density and speed of the place. In big cities, it seems like everyone is already in a rush or in the middle of something, so folks may be scared to "interrupt" or disturb strangers, even if it would make their day. In smaller towns, that kind of vibe may not exist as much.
The entire Maritimes region in Canada. Just go to a pub, raise your glass to someone and you’ll have a roomful of friends in minutes. So friendly it brings a tear to the eye.