I don't know if I can answer that; maybe a few more years of researching transition will lend me more confidence to take on questions like this.
I can, however, speak to the reason (or reasons) why it seems like this: the PCA is organized specifically to be a grassroots denomination. This leads to ancillary factors which contribute to the problem.
When the PCA was formed in 1973, much of the impetus for its formation was the direction and leadership of the Presbyterian Church in the United States (PC-US). The direction of the PC-US was objectionable because, over a number of years, they had moved further and further away from holding the Bible as authoritative, inerrant, infallible, and inspired by God, leading to increasing theological liberalism. The leadership-- a top-down, authoritative oligarchy-- was objectionable because the structure of that denomination did not (at least in the eyes of the dissenters) allow for fair dissent or dissolution. Thus, when the PCA formed out of the PC-US, they decided that the structure would be somewhat reactionary, and went with a grassroots organization.
The result of this is that the larger governing bodies of the PCA have little or nothing to do with the arrangement of a pastor's call. The General Assembly normally has no part in the process (though there have been a few occasions when a congregation wishing to dissolve a relationship with a pastor had to go all the way to the G.A. level!). The Presbyteries have some part, but that part is nearly too late to have any effective leadership role.
Presbytery involvement comes into play only after a call has been issued to a candidate-pastor-- so the whole system of the candidacy process can be completed (or nearly completed) without the knowledge or participation of Presbytery. The role of the Presbytery's involvement comes in just a few forms: approval by the receiving Presbytery of the candidate-pastor himself with regard to ordination (he must either be ordained by that Presbytery or his ordination must be approved to transfer from another Presbytery); approval by that Presbytery of the terms of call as given by the church issuing his call; and dismissal from the previous Presbytery (though this step is unnecessary for a new ordinand). Everything else is left to the local church.
What's missing (that my friend pointed out) is accountability for the pastor and guidance for the church:
- No one questions the pastor about why he is leaving his current call. Has he finished the work God brought him there for? Is a bad situation truly unreconcilable? Is he missing something that he should know?
- No one offers an objective assessment about what he is suited for. Has he considered (or reconsidered) his sense of calling thoroughly? Does he have a clear vision of what God is leading him to do?
- No one offers an objective assessment about where he might go. Is the church that extended him a call the best fit for him? Is he the best fit for that church?
- No one has given any leadership or guidance to the churches in their search. Have they consulted with anyone about who and what they are looking for? Do they know how to conduct a proper search? Have they considered the best candidate-pastors for the position?
Soon I'll post my thoughts on some solutions.