I would like to begin with a passage on American history I've often quoted, and which I believe provides an insight into a crucial underlying thread in the American mindset:
But doctrinal orthodoxy was the not the only measure of a man’s fitness to govern, as Winthrop learned to his cost. His natural authority was based to some extent on his descent from the old squirearchy of England, and his manifest possession of means to keep up his station in the New World. In 1639, however, Winthrop discovered that his English agent had cheated him, and that his affairs were in a muddle. The agent was convicted of fraud and sentenced to have his ears cut off. But that did not get the governor out of his financial difficulties. He found himself £2,600 in debt—a formidable sum—and was forced to sell land on both sides of the Atlantic. His financial plight became obvious. Friends and political supporters rallied round. They collected £500 to tide him over. They donated 3,000 acres to his wife. But Winthrop’s opponents pointed fingers. The Puritans did not exactly insist that poverty was a sign of wickedness. But there was a general assumption that the godly flourished and that if a man persistently failed to prosper—or if financial catastrophe suddenly struck him—it was because he did not, for some reason, enjoy God’s favor. This idea was very potent and passed into the mainstream of American social consciousness. Winthrop was its first victim. In 1640 he was demoted to deputy governor. Some purists even proposed to ban him, and another unsuccessful man, from office for life, `because they werte growne poor.’ But this measure did not pass.
- Paul Johnson: A History of the American People
"the godly flourished... if financial catastrophe suddenly struck him - it was because he did not, for some reason, enjoy God's favor."
The prosperity gospel as such has very deep roots in the American subconsciousness, there is an unconscious association between godliness and material, bodily, and physical flourishing.
As we know, the concept of virtue or excellence is not restricted to what today we consider to be "moral". It encompasses any sort of life skill and there can be excellence or virtue in cooking well, crafts, fighting, etc. However this raises the question of whether it is the preacher's role to teach their congregants to "live well" in some very general and broad sense, to encompass not only morality and the fruits of the spirit but also how to have a great marriage, career, etc, etc. Remember, the American mindset is that, somehow, godliness is associated with financial and vocational competence, arguably St Paul may have hinted at this when he spoke of a person who is unable to materially provide for his family as being someone who has denied the faith. There appears to be a deep link between material, economic, and physical competence and "virtue" or "living well".
This however seems pretty awkwardly juxtaposed against the image of Christ and Christianity as generally being a religion for the weak, poor, sick, etc, etc. We instinctively react against the prevalent American pastor-as-life-coaches, with immaculate appearances, well chiseled physiques, winning go getter corporate climber attitudes, etc.
This may however just be a particular phenomenon of American disestablishmentism in general. In most other parts of Christendom, the clergy were mostly drawn from the intelligentsia, the Oxbridge Don and Fellow as clergy, their primary role was intellectual preaching and communication of the faith. To be sure they needed some minimal respectability and "competence" in living, but they were not considered life coaches. All parts of Christian society were expected to participate in the role of teaching Christians how to live well. Remember that in the Church of England the king was technically the head deacon whose role was precisely to be the "material" body of the Church and to serve the Church material needs, presumably to be that "life coach" and material role model for the Church. Once the Puritans went to America however this division of labour was gone, Puritan preachers themselves were expected to take on the "life coach" role of the king and thus were the two offices, the intellectual and the material, amalgamated into the role of pastor who now needs to become life coaches when the King no longer served that purpose in the Church.
I'm not sure if this is inevitable in polities with disestablished churches. I think the distinction between teaching and leading elders in the Presbyterian church was made to preserve the distinction between the two roles, teaching elders would handle the preaching and teaching side of the ministry, while ruling elders did the "life coaches" part of the ministry, but generally, there is a substantive question to the extent to which Christianity is meant to teach its congregants to "live well", and to what extent this extends to material and physical dominion.