I'm leaning more towards war guilt and misplaced pride in Article 9 than strictly cost.
I, too, initially thought that political reasons were the primary factor.
However, the more I looked into it, the more I felt that the issue largely came down to cost.
Japan's military procurement planning at the time followed a process of first compiling a "wish list" and estimating the costs, then trimming the list down to fit the available budget.
If the exclusion had been due to political factors, the obstruction would presumably have come from the Defense Agency's internal bureaus or high-ranking bureaucrats; however, looking at the outcome, it was high-ranking naval officers who blocked it.
For starters, the senior officers were not even reporting the matter up to the high-ranking bureaucrats in the internal departments; they were voluntarily cutting the items as a result of prioritizing within the budget.
To add a point regarding this: securing the budget was the job of high-ranking bureaucrats, whereas the details of budget execution were determined by military officers.
There is a well-known figure named Osamu Kaihara（海原治）. He was a high-ranking Defense Agency official and an advocate of a "small-scale armed force"（日本列島守備隊論，） doctrine—a radical stance that put him at odds with military officers.
However, although Kaihara obstructed the securing of the budget, his influence did not extend to the actual procurement of equipment; consequently, the Self-Defense Forces were able to purchase the items they desired, even if only in small numbers.
Since Japan’s economic growth was partly due to Kaihara’s cutting of the Defense Agency’s budget, I will not pass judgment on whether he was good or bad. All I can offer is my own speculation based on the facts.
※Kaihara’s theory on the Self-Defense Forces was essentially a "toy theory"—arguing that since the SDF would be useless in actual combat anyway, resources should be prioritized for the Ground Self-Defense Force rather than the costlier Maritime and Air branches.
He advocated for a "Japanese Archipelago Defense Force" model: the SDF would possess no expensive equipment suited for overseas expeditions, the Maritime Self-Defense Force would be restricted to coastal defense, and the focus would shift from frontline weaponry to logistics and stockpiling supplies and ammunition.
Defense would rely on a "Homeland Defense Force"—a militia organized from citizens who had undergone a period of military training—to resist any enemy forces that managed to land on the mainland. He believed that low-cost armaments were sufficient.
Uniformed officers who heard Kaihara expound on this "Japanese Archipelago Defense Force" theory were reportedly outraged, feeling he was treating them with contempt.
