In this story, dungeons appear and monsters start coming out, but the monster parts and cores are completely useless, so nobody has any incentive to kill them which in turns lead to the whole country being overrun and fucked over because nobody could be arsed to actually control the monster population (I will blame the government incompetence on the coup that happened). Then on this chapter we see that a weapon made with monster cores is actually very useful, so what the fuck, there should be at least an adventurer gear industry in that case.