I had the same question about the prisoners turning on the guards. I believe that these prisoners were not easy to come by. Keeping them alive gave them a valuable human resource. It seems like to me, if the guards had to shoot all the prisoners, they would have shot themselves out of a job. Thus, shooting prisoners would have been a last resort scenario they would not want to make. Also, I wonder where the Japanese would be if they shot all those coal workers at their distribution hub? They would have been without coal. That would be like shooting themselves in the foot.
I was thinking of the Warsaw Ghetto. There a small number of Jews tied up 36 German officers and 2,054 men. It is estimated that 300 German soldiers were killed.
The men in these Japanese camps were so brutalized, I am surprised that they just didn’t turn on their captors and attempt to exterminate as many Japanese as possible.