Having to share a home with roommates is, I think, a product of the split of the
American family structure. This split could have originated from
immigration as people slowly began breaking off from their families in their homeland and traveling here on their own, but modern trends play a more visible role in single young people's lives today.
In the past, when men left his parent's house, it was typically to build his own home, marry and raise a family, or step out to make his own name and fortune, as Americans have always set out to do whether they are good at it or not. Women were usually married out of their parents' house and sometimes, if they were never married, they never left. With the eruption of equal rights, a lot of that changed. Colleges were becoming co-ed and even though at the outset college was looked at only as a grooming school for marriage, women were at least going.
Speed up to the present. It is now standard in America that no matter how ready or prepared, focused or educated a person is, when they hit the age of eighteen and hopefully have graduated high school by then, they are expected to move out on their own at some point in the near future. Aside from being one of two benchmarks for adulthood, this standard age was no doubt hastened by the swells of colleges and available extended education and training, to the point that college is something almost everyone is expected to attend. It has become the raised standard that is intended to make us feel as though we are progressing as a nation but I see it as a formula for creating a nation of transients.
One of the options that works to connect us after having been boosted from the nest is to find a shared dwelling. This is also usually due to financial constraints while either still enrolled in college or suffering the eternal financial burdens that immediately follow (oh I'm sorry they do give you 6 months to get started on those payments you'll be making for the next ten years-my bad) graduation.
Roommates can and often do become a surrogate family; sometimes it can be even better than your original family and at other times it is so bad that you couldn't get back into your old room at mom and dad's (that's likely been remodeled into an office since you left) fast enough. They are the byproduct of a society that is hell bent on isolating all of its members so that the only sense of community is one created out of the void, created because the structures that had once been reliable are not even standard, let alone reliable. Roommates are a coping strategy, and it has become much more a standard of living than even the family structure is today. That, in a way, is scary and even saddening, but I'm not close with my own family, so I figure I'm not missing anything.