In "The Upper Crust of Progressive Episcopalians", by George Will is this key insight:
“The Episcopal Church once was America's upper crust at prayer. Today it is "progressive" politics cloaked -- very thinly -- in piety. Episcopalians' discontents tell a cautionary tale for political as well as religious associations. As the church's doctrines have become more elastic, the church has contracted. It celebrates an "inclusiveness" that includes fewer and fewer members.”
It seems people want to belong to a church or organization that actually stands for something rather than for the acceptance of "whatever". When there is no distinction between the church and the culture, what appeal does the church have? Why bother to attend church? Or, as in George Will's column, why bother to stay connected to that church when you can become part of one that helps you become better than the culture?