Because we are closing down the public sphere. No agora (market places, parks, et cetera), where people can walk around, run into each other and chat. All these places are "too expensive", thus all kinds of fancy projects are realized instead. What a waste of community money.
In my home village, there are 6 soccer fields. 4 of them are never used, but are inaccessible to anyone who may want to play for simple enjoyment. As youth cannot do anything, youth misbehave (as they have no place where they can actually DO something). As a result all kinds of projects are started to dump them in the middle of somewhere. Huge expenses, but don't expect much return. Yay to the lawyers
; yay to the people who prefer not to invest in our youth
.
Another issue is scale. If you ever lived in a rural area, you know that it is normal to greet everyone in the street. You know everyone, everybody knows he / she is part of the community. Not so in cities.
Time is everything these days. Especially on the job, but that of course applies to off the job as well. As friendliness costs time, it is uneconomical, and people don't engage in it too often.
Why do people laugh a bit, when a loved one has a minor freakish accident happen to him / her? (eg. dropping a pan to the floor)