Ben, you can rewrite the initials for just about every one of the 7 mainline denominations and the story will be the same. They all have conservative congregations and orthodox people. But, whether from ignorance, denial, wishful thinking, or willful blindness to reality, they stick with their denominational "family" in all of its dysfunctional splendor. For some of the older pastors, I speculate that retirement pension plans enter into the calculus. But, in most cases there is an unwillingness to face up to how bad it really is.
Ten years ago the judicatory (aka district) that my congregation belonged to withdrew from a mainline denomination. This amounted to about 150-200 congregations, some of them with 5k to 8k on a weekend in attendance. We thought that some of the other 34 judicatories might follow suit. They did not. During that same decade, the chair of our educational ministries department (the strucutre had three boards: international missions, national ministries, and educational ministries) on the national board was an openly gay associate pastor in one of the congregations. He was also a member of the planning committee for several of the national conventions, on the executive committee of the denom, on the search committee that selected the paid head of the denomination, etc. His story was documented in the secular press where he volunteered quotes. So this was not a case of "outing" a closeted gay man. The president of the ministers council in one of the state associations for the denomination was an open lesbian who got married to her same sex partner while serving in her post. More than one of the judicatory execs assuaged their disgruntled pastors and laity by assuring them that the claims of gay ministers in the hierarchy were untrue and assured them that nothing of the kind was happening. So who do you blame, blind sheep or blind leaders?
In most of the mainline denominations, the situation is worse than the critics claim. Yet, biblical admonitions of unity are regularly invoked to quiet the critics, dismiss the evidence, and temporize the circumstances.
The solution for survival in this particular denomination involved mortgaging the corporate headquarters (a valuable piece of real estate) to the pension board and the international ministries board of the denomination coupled with a restructure plan that allowed for the balkanization of the denomination. Individual regions became more independent, the central office became less powerful, and regional execs were able to distance themselves from the more controversial aspects of the denomination.
To date, the denomination continues, weakened, but still functioning after a fashion. Conservatives hem and haw when asked why they stay. The blessing of unity, the opportunity to bear witness, the hope of "making a difference," fear of becoming a fundamentalist schismatic, and sheer inertia all drive the impulse to remain. Ben, you are so right.