No matter the slaughter, they could never be completely annihilated, nor could they be completely killed off.
After all, one couldn't always go to the Lower Realm to slaughter, right?
"As for that, the Prison Demon World has many unique materials. Apart from Nullifying Metal, there's also the Sound Pattern Web. It's said that this Sound Pattern Web can release powerful sound waves which solidify into substance; its might is no less than that of ordinary Magical Treasures. Even a mortal who obtains it could possess battle strength not inferior to a Qi Practitioner."
"There's also the Demon Sound Shell, a special natural shell that can enslave others and take over their minds by releasing a series of entrancing Demon Sounds through the tapping of the shell."
