Chasing Demon's words were on point.
It was clear that the copying technique was extremely powerful but that it also expended large quantities of Credits or other items containing "Breath" to work.
Reproducing the might of a rank 5 magical beasts wasn't a cheap task, it was clear that the reserves of the underground organizations would be drained in a prolonged war.
Yet, as long as those reserves existed, the Coral archipelago was virtually unbreachable.
Also, the only way to deplete those reserves was to force the activation of the copying technique, meaning that the armies from the continent would have to fight a seemingly endless tide of magical beasts in the meantime.
The underground organizations wouldn't have a chance to defend the islands for much time if the three big countries decided to keep working together but the archipelago wasn't exactly their main focus.