Why Dead Balls Are the Only Controllable Phase
A corner or an attacking free kick reduces football to a set of fixed inputs. The delivery point is known. The defensive shape is visible and static before the ball moves. The attacking side can choose which bodies stand where, which means matchups can be selected rather than inherited from the flow of play. Nothing else in the sport offers that combination, and nothing else can be practised with such fidelity to how it will actually appear.
The other half of the argument is frequency. Corners and free kicks in dangerous areas arrive in almost every match, which turns a small per-instance edge into something that accumulates steadily across a season. Set pieces also compress the value of physical traits a squad already has: height, timing in the air and strength in contact all convert directly, without needing the technical polish that open-play chance creation demands.
