Eventually, the Boston Red Sox will dispose of prospects that were once highly rated, but have since stalled or regressed. This is a very natural process in baseball as talent reaches a certain level, usually Triple-A, and simply stalls.
Another generality is the prospect is exposed to major league baseball and just cannot adjust to that level. Weaknesses are soon discovered by the opposition or on clear display by themselves.
A few years ago the Red Sox had several prospects that were easily in their top ten or very close to it. Garin Cecchini, Sean Coyle and Anthony Ranaudo all were coveted by Red Sox fans as future mainstays – all are gone.