This blog post suggests that people are leaving the church because many sermons are polished, but are theoretical and lack the gospel:
Why are people leaving good, established, traditional churches with great facilities, full of quality individuals and extensive children’s programs to attend churches that meet in old schools? Because their pastors have fallen into this trap of theoretical preaching. Therefore, the message is no longer relevant. The pastors are not communicating the life-changing message of the gospel. They are delivering well-polished lectures with biblical points. People know the difference and they vote with their feet.