Why Japan did not disperse warship construction

Did the Imperial Japanese Navy try to build ships outside the Japanese home islands, especially in resource-rich occupied territories?

Not to a significant degree. Singapore could have supported some construction and Korea could have hosted expanded yards, but money, policy, and a preference for employing Japanese workers limited that approach.

Singapore had facilities theoretically capable of building ships, particularly escorts. Additional yards could also have been established in Korea. Funding limited what could be done, and the desire to disperse construction was weak. Treating these territories as vassal states and wanting to employ Japanese workers discouraged the expansion.