Growing the Mainline
I do have some thoughts that I envision writing down concerning the mainline and campus ministry in general. But for now I'll rely on the excellent comments on the lack of growth made by Chris Tessone.
More and more mainline kids are going away to college, leaving behind their families and faith communities at a critical juncture in their lives. When they arrive on campus, chances are there is no campus ministry run by their denomination.
If there is such a campus ministry, chances are good that it's underfunded, understaffed, and does not advertise itself well. In some cases, it does not offer weekly worship and Bible study, meaning it doesn't resemble a Christian community at all.
When mainline Protestant kids are at the critical point in their lives of reassessing all the influences they received from family and community, no one who speaks to their religious background in helping them integrate faith with what's new in their lives.
These kids will either leave the church altogether or will probably convert to Catholicism or join an evangelical group. They will not return to mainline Protestantism as their parents in the baby boomer generation did.