For the war plan that the Imperial Japanese Navy (IJN) created in the 1930s and largely practiced during the Pacific war, anti-submarine commerce would only become important if their war plan had already failed.

Starting in 20s and 30s the IJN war fighting doctrine began to fixate on winning a decisive battle with either the British or American battleship fleet close to the IJN's own bases in the Western Pacific. This plan and it's associated doctrines was grounded in their 1905 experience at the Battle of Tsushima in the Russo-Japanese war. Another reason a decisive battle was a key element of the Navy's war plan was that they knew an attritional style of warfare would put them at a severe disadvantage. Japan's economy was largely agrarian, 50% of it's workers in 1940 were farm workers, compared to 22% for the US. This meant that (despite it's first rate ship and aircraft technology) the industrial sector of the Japanese economy was quite small, and relatively undercapitalized. Given this, a short bloody war was a relatively rational strategic choice, although Japan lacked a means to compel the U.S. and U.K. to likewise avoid an attritional strategy, dooming the approach to failure.

Anti-Submarine Warfare and convoy battles are inherently attritional. The submarine commerce raiding strategy works if the subs can sink more tonnage than the adversary can build each month over a long period of time. Conversely, the convoys win if they can either avoid being sunk in sufficient numbers or sink more submarines than their adversary can build. This type of war obviously massively favors the side with the larger industrial base. This wasn't Japan and it wasn't Germany.

So why not do both? Plan for a big battle and also get good at protecting convoys? Simply put, Japan and the IJN was intensely resource constrained. They didn't have the money, time or industry to develop both doctrines. A technical team that you allocate to developing torpedo bombers and dive bombers isn't allocated to developing ASW patrol aircraft. Pilots only have the time and fuel to fly so many training missions in each specialty. Training for destroyers and cruisers costs fuel and time, if you conduct a night torpedo attack exercise, you're not conducting ASW exercises with those resources.

What the IJN did allocate resources to were techniques that would help them win the big battleship throwdown they based their war plan on, and except the battleships themselves, these techniques paid dividends. The IJNs effective carrier air arm and land based attack aircraft were designed to cause battleship attrition before the large surface action. The IJNs training in night torpedo attacks was designed to likewise inflict battleship losses prior to the main battle. The Yamato class superbattleships would be a trump card. These key tactics and techniques crowded out time or resources for ASW training.

The IJN chose to specialize in tactics that fit their overall plan to win the war. They avoided "frittering away" resources on activities that did not contribute to this plan. When the war turned more attritional than the IJN expected, they had to improvise ASW with whatever was leftover. On top of that, they were husbanding scarce resources for a big surface action all the way up thru 1944. After they decisively lost the 1944 battles of the Marianas and Leyte, they had almost no resources remaining to do anything with.