The obvious answer is that they are not meeting the needs of their members. Amongst all the various programmes that churches create, they miss the simplicity of the spiritual need, both to give birth to Christ in them, and to ongoingly nurture the implanted life.
There is a failure to recognise that many are simply going through the motions of being a Christian, because of a lack of deeper understanding that is necessary because of the complexities of today’s society and the many technological advances that help to muddy the spiritual waters. People’s basic need is to be set free and then to maintain that freedom. This should be the churches main aim.
The structure of some churches does not permit the minister/priest/pastor to have power over what takes place. Committees and management board structures often take precedent over spiritual needs and demands. The spiritual leader of the group should not be restricted in any way when delivering a message from the pulpit. He has more potential power than the president of the USA because he is delivering messages from God, and he should not feel the need to follow any other sources other than that which he finds in the Spirit.
In some instances it is the “old school” in the church who maintain a grip on the running of things and who refuse to vary from the old ways, and also who unfortunately at times like the power that they have. So the Spirit is locked out, unable to “heal” the ailments which grow worse as congregations age and young people particularly find no relevance in what is happening (or not happening).
There may also be mismanagement of the finances, due to blind refusal to examine what is and what is not necessary, and a seeming desire to maintain the status quo for whatever reason, which again may be unwillingness to change. Recovery from all of this is simply a matter of listening to the Spirit of God, and bringing the message of life afresh in new and relevant ways, instead of tired old set programmes of bible chapter and verse, as is so often the case. Music in the church also is an indicator of spiritual health [or not], as it corresponds with and promotes worship and spiritual freedom of expression. Playing old hymns that no one knows the words to is a worship killer. [Some hymns are really good].
Preaching and teaching are the essential mechanisms for a soundly based and “alive” church. The measure of success in this can be gauged by any of the individual members satisfaction with their spiritual progress, and by the obvious [or not evident] love in the place.
It should be noted that all the above only refers to “normal” churches, that have the accepted concept of grace. “Legalistic” churches which are still stuck in law concepts may actually have viable congregations because they are still closer to “the flesh” and, “wide is the gate”.