In 1941-42 our strategic bomber force was small, massively engaged in Europe. And frankly amateurish and learning the ropes.
After years of hard won experience in Europe, and with FAR better aircraft in the B-29, Japan was very difficult to bomb with the same effectiveness.
It’s kinda interesting how fast tech was advancing in the day. It wasn’t long after the war that we could have bombed Japan with bombers launched from the US mainland using b-36’s, with massive bomb loads. And the Japanese fighters couldn’t have touched them.