Why Japan kept its inadequate 25 mm antiaircraft gun

Why did Japan keep fitting an ineffective 25 mm antiaircraft weapon late in the war?

It knew the weapon was weak but lacked practical alternatives and the industrial capacity for rapid retooling.

The problem was not ignorance: Japanese officers understood that their light antiaircraft weapon was inadequate. Britain and the United States could turn to other systems because they had alternatives in production or the infrastructure to expand them. Japan had committed its limited industrial resources elsewhere and could not retool quickly once wartime demand became urgent. Continuing to fit the weapon therefore reflected constrained replacement capacity rather than confidence in its effectiveness.