With the range of US bombers, island hopping was required to get in range of the Japanese mainland. Why, with the USSR as an ally, were bombing raids not conducted from the USSR, which was well within range? I know the USSR was engaged in battles like Operation August Storm with Japan late in the war. Was there a reluctance to have US forces inside the USSR?
More then that. It was that Japan and the USSR had a full on armistice and they basically didnt provide any meaningful aid to the US/Commonwealth. For instance multiple B-29 crews who were forced to land for safety at Vladivostok were actually interned for months and their plans confiscated and studied for Soviet benefit.
Why, with the USSR as an ally... I know the USSR was engaged in battles like Operation August Storm with Japan late in the war.
"Late" is the key word. The USSR was not an ally in the war against Japan until August 1945. The USSR and Japan had signed a non-aggresion pact in 1941, and that had remained in effect for the bulk of the war, until the Soviets denounced it in April of 1945 and declared war on Japan in August.