Because an infantry invasion of Japan, would have resulted in <em>Far</em> more casualties for both the americans and the japanese. Than the dropping of an atomic bomb.
During WWII, George C. Marshall served as chief of staff of the US army from September 1, 1939 until November 18, 1945.
During his tenure he helped train US soldiers in modern warfare as an instructor at the Army War College in Pennsylvania.
He inherited an outdated and poorly equiped army, so he was also responsible for the modernization of the army and co-ordinated a large scale expansion of the military.
While Marshal wrote the document that would become the central strategy for Allied operations in Europe, Dwight Eisenhower would become the Supreme Commander of Operation Overlord.
