Congregations tend to be output based. As such, they want the growth numbers of the church to be better each year than the year before. They want to attract new people to provide leadership where needed and to contribute generously to the church budget and any debt.
By their second generation, many congregations are composed of people who come from a churched culture and do not understand the unchurched culture. Even if they became professing Christians during the past generation, they may have lost the perspective of the unchurched.
The geographic context served by congregations often changes from generation to generation. The demographics within active congregations may not match the community context, if it ever did. Congregations can become disconnected from their context and not understand the people.
The theology, philosophy, methodology and style of congregations can drift over the years. One day, the long-term members realize this is not their congregation any more, and they seek to bring the congregation back from the abyss instead of seeking God in the present times.
Congregations can get stuck in place, lack innovation and creativity, and simply become dull. There is no excitement, glitter or pizzazz. As such, they are unattractive to new people and do not inspire existing participants to do more than to go through the motions of being and doing church.