If no Presbyterians are moving into our town, then the Presbyterian church will likely be declining. The movement of people is one ingredient. Societal changes are also part of the answer. I am inclined to think that the biggest factor is something much simpler. Dominant and denominational positions are inherently passive.
Distinctive position is active.
But society changed, and with it changed the role of religion in American life and the position of churches in society. Now the church is marginalized from the mainstream of society, and social forces move people to other institutions, movements, causes, and activities. Any church that is passive will dwindle and die. Active churches, which reach out to persons, offering a distinctive expression of the gospel in word and program, will tend to grow. This has been demonstrated even in very rural areas, especially if the hurts and hopes of unchurched neighbors are part of the church's mission.