Why Japan did not prioritize more convoy escorts

What limited Japan's ability to build more escorts before and during the Pacific War?

Engines were not the main obstacle; yard allocation, Army-Navy control disputes, and Japan's short-war strategy made large escort investment unattractive.

Small escorts could use machinery similar to that fitted in fishing vessels, but producing them still meant diverting yards and resources. The deeper obstacle was strategic: Japan expected a long war against the United States to become unwinnable, so investment in convoy protection conflicted with its emphasis on a quick decision. Britain's blockade strategy, by comparison, assumed from the outset that maritime war would be prolonged.