For many people, the status quo is very valuable. They will discount greatly any future benefit that may come from its disruption, even when the benefit to them is certain.
The creation of community, however valuable, is disruptive. It requires new habits, new relationships, and a new sense of identity.
Because of the great value placed on the status quo by so many people and because of the essentially disruptive nature of creating new community, in the absence of a serious crisis, the vast majority of people within any given community, who have sufficient resources, will prefer to preserve the status quo rather than risk disrupting it. For this reason, most people will prefer to stay a member of their current community rather than join a different or new community. They will only join a new community, if it will very easily make them much better off. As a result, because new communities rarely have many resources, the people who are most likely to create, join, and contribute to new communities are those people who are marginalized in their present community or unsatisfied with it.
As our society gets increasingly wealthy, I think more and more people will judge that there is little or no incentive to seek out or create new community. Fortunately, as our society gets increasingly wealthy, those who are willing to gamble on the possibility of new community will have more resources at their disposal than ever before. As existing communities become increasingly homogenized and rigid, perhaps, for some people, new, heterogeneous, and dynamic communities will seem much more valuable and, therefore, worth the gamble.