Why would they need to? Japan’s strategy was to send numerous bombs rather than a few larger bombs. These bombs were not finely targeted weapons. Japan didn’t have weather satellites. More and smaller bombs increased the odds of success. Just because Japan uses smaller balloon weapons, it doesn’t mean they were not capable of doubling the size of the balloons. You seem to think the Japanese were incompetent dolts. They were and are anything but that. Well this gets to the point that I have repeatedly ignored. Neither Japan nor the US knew how far along each was in the development of nuclear weapons. Japan falsely thought the US was further along in nuclear weapons development because they believed the testimony of a tortured American pilot. No there were not, but neither side knew that. You are assuming that the decision makers on both sides knew what we know today. And that just wasn’t the case. Well rather wasting more of my time, how about you doing some googling? I think you answered your question as to why Japan made smaller balloon bombs. But nuclear weapons would have made larger bombs worthwhile for Japan to build larger balloon bombs. Well, that isn’t clear. But, it would have had an effect on Allied forces invading Japan. I’ve already outlined how Japan could have used nuclear weapons on Allied forces during an invasion of Japan. Up until Japan’s surrender, Japan was still conducting attacks on Allied forces. Well, just because you cannot wrap you mind about remote detonation of weapons, it was a well-established technology at the time. If Japan had detonated a nuclear device on Iwo Jima, they would have killed a lot of people and would have repelled the Allied invasion and that was Japan’s goal. Japan wanted time to recoup, a Japanese nuclear weapon would have given them that time and it would have made the war much more costly in terms of lives lost and mutilated bodies. Just because that fact runs counter to your beliefs, it doesn’t mean it isn’t certain. It’s a fact. Japan could have easily delivered nuclear devices on Allied targets, if it had nuclear weapons via the previously mentioned delivery vehicles.