This is NOT a SBC issue, its a problem with Christian Churches period in America...
Poll after Poll supports that a solid majority of every bible based Church loses large part of the 20 somethings, almost as after Youth group go right out "into the World" so there is an absense of that age group in most churches...
many do come back to Church in 30s , as if once started families, careers, decided to have God back in their lives...
Think ONLY real cure is to have the peaching/teaching be 'geared" to their particular needs/fears/views of that Age, and how God and His word IS practical and useful to them
Its like they are the "invisible/lost" peoples group in Church!
Are you making the assumption that the Fundamentalist churches are not teaching the Bible? They got plenty of people and lots of young people. Fundamentalist are more conservative than conservative SBC churches, and are more exegetical in general. Its thus they are separatists.