A diamond setting has the same goal as an inlaying, which is to emphasize the stone in an aesthetically pleasing way. However, this needs to be done differently for different gems, because they do not all share the same inherent qualities. Setting essentially ties the gem onto the metal of the band from the bottom, or at an angle.
Inlaying, by contrast, inserts them into the metal so that only the top is left visible. A craftsman setting a stone would prioritize it over the metal. This means the structure of the latter gets decided based on the gem’s dimensions. The stone is adjusted by molding the band metal around it, and adhesives are never used.