Some church traditions have a long history of spotlighting "trophy" converts as a means of gaining an edge. Perhaps the most publicized competition has been between Anglicans and Catholics. The defection of John Henry Newman from the Church of England to Rome remains the biggest headline in that tug-of-war.
The reasons why followers of one church jump to another are myriad. As the great sociologist/theologian H. Richard Niebuhr, social and economic factors are among those that have loomed large: in the "Social Sources of Denominationalism" he outlined the upwardly mobile process.
Niebuhr said that American church groups were arranged in a kind of hierarchy of class and prestige. If you began life as a poor person in a fundamentalist church, your education and spunk might lift to you a higher economic group which would, in turn, incline you toward a church that reflected your new status. And so on.