I would hazard a guess that its more common in apartments to be socially distant. Because you are far more likely to get annoyed by the neighbour being noisy, you don't have any windows to interact through with them (eg. waving) and most important (imo) of all: you can't just talk in the hallway/stairway the same way you do in a garden or across a fence. And actually entering someones quarters is probably a lot more socially taxing than just stading in their garden.

What do you reckon?