Why in the hammer throw you throw a stringed weight instead of an actual hammer?

The hammer throw was originally thrown with a sledge hammer, but as the sport developed people made the implement more effective by putting the weight as far away from the thrower as possible without violating the rules of the hammer's meassurements. The thrower's bodyweight counters the hammer head's weight (caused by the centrifugal force created by the moving of the implement) making a circulare motion. If the radious is larger (the implement's centre of gravity is as far away from the rotational axis as possible) a longer throw will be produced.