Churches merge out of weakness, not strength. Every liberal denomination is dying. The more liberal it is, the faster the decline in membership. The Methodist and Anglican church bodies are dead men walking. Since these church bodies abandoned traditional Christianity decades ago, the only way that they can defend their existence is through membership and property. They merge in an attempt to increase the membership numbers. You see this in the ELCA. You merge with several dying churches to make your numbers look bigger. Money and property are the new marks of the church.
Reading that, I realized you could exchange the word "churches" with "religious orders" and end up with another statement of fact. (see the thread on dissident nun Sr. Joan Chittister)