That can be mitigated by having a common space outside, as well as having similar setups next door so that, while you might not see others in your own building,

That can be mitigated by having a common space outside, as well as having similar setups next door so that, while you might not see others in your own building, you'll be able to wave at people next door. And if enough people do that, and then go down to meet them in person, you'll start bumping into your own building-mates. I'm not actually describing theory; I have a friend in Sweden who has made friends this way.