Certainly that is part of it, but I think a bigger part of it is that finding a group of people you'd like to live with a space that enables communal living is

Certainly that is part of it, but I think a bigger part of it is that finding a group of people you'd like to live with a space that enables communal living is really hard. Therefore developers build for the plug-and-play self contained dwelling. Stated another way, the prevalence of independent living is more a consequence of high "coincidence of wants" costs and not of preferences. https://en.wikipedia.org/wiki/Coincidence_of_wants https://en.wikipedia.org/wiki/Coincidence_of_wants