I think we have a naively rose tinted picture of the past. Most people shared their space within a community in the past not because they liked that place or the people they shared that place with, but purely out of necessity and not knowing it any better. Back then there was no easy means of getting new outside information, and even if your place in your community was somewhat uncomfortable, it was still something you knew. You knew what to say, you knew what not to say and to whom and so on.
So leaving that community was not something people easily did. But they did, because of resources and money, people migrated from their rural communities into the cities, families torn apart, the industrialization brought with it a faster flow of information. People got to know the world outside of their communities and realized that they liked it more. So instead of huge family clans we had small atomic families now, with grandparents living in their own atomic household, often somewhere else. Young people who went to find themselves in the cities lived alone or in loose collectives or flat shares with strangers (usually with the goal to get your own thing as quick as possible).
In western societies that new freedom and individualism then (like so much else) got hijacked by capitalism. Ten people living together only need one hairdrier, ten people living seperated need ten hairdriers (insert any other appliance/product you can think of here). People living alone is good for capitalism, which is why it has been marketed as a dream. Be yourself! Fuck the others! Get your own hairdrier! Live alone and die alone!
Like fish in water we internalized these values so much, that we don't question them. In the US especially those values have become architecture to a degree, your literal world took the shape of this individualism [insert suburbia.gif] – how to start living a collective life in a individualistic environment, where without your personal movable 8m² of space you are cut off from any meaningful function society provides you with?
Especially in the US people live in spaces that favour individualism to such an degree it is the simple comfortable default. If you want to change that you have to work against the forces that exist.
Why has this changed?