Why Japanese submarines achieved less commerce destruction

Why were Japanese submarines less effective than American submarines in the Second World War?

Doctrine prioritized warships, and geography put worthwhile American commerce targets much farther from Japanese operating areas.

The first limitation was doctrinal: Japanese submarines were directed toward fleet targets rather than sustained commerce warfare. Geography compounded that choice because the United States' main trade routes lay behind the advancing front, forcing Japanese boats toward the Indian Ocean or deep South Pacific to find shipping. American submarines, by contrast, could attack traffic essential to Japan close to the operational theater. The answer also notes that successful British submarine pressure could divert German traffic onto railways even when sink totals looked smaller.