Very relevant topic and interesting comments.
I think that there are several factors. One is that, in most of the "traditional" denominations, distancing behavior over time by younger parents has resulted in far fewer young people being involved in highly relevant Sunday school - and thus, not moving into church attendance and leadership. Not so much a factor in situations where the churches are more evangelistic and not dominated by denominational aspects.
As some have posted - other strong factors as well.
For reasons noted here by others, and other reasons as well, it is not difficult to understand why otherwise thinking people have distanced themselves due to inconsistencies/corruption/falsity in various organizational hierarchies. Most organizations by humans do this to themselves. Such propensity is Biblical.
One huge bonus over time may be that most true Christians will live the fact that Christianity at its root consists of a personal relationship with the Savior and a Triune God, and will demo this in their daily lives. And, with realization that willful and strengthening fellowship with others is a secondary, although often important, activity.
Then again, maybe I am way off base.
