Congregations seeking to transform are not only concerned about people who leave the congregation and people who stay with the congregation for great reasons. They are also concerned about people who stay with the congregation for dysfunctional reasons. These people often have a negative influence, and while in one sense it might be better if they left, in another sense turning them around has great value also.
Some people do not leave because they feel stuck. They do not know where else to go and/or there are not good alternatives in their area. So they just stay and are unhappy.