Compared to the Demon King, the human race's corruption and slavery were even worse than him.
After all, the Demon King was forced to be a shut-in in the Demonic Impure Lands. The Demon King couldn't leave the Demonic Impure Lands even if he wanted to since only after all the heroes had died he would be granted freedom.
Because of that, the heroes had already forgotten about the existence of the Demon King since they were too busy with cleaning up the corruption and slavery within the human race.
So rather than becoming mercenaries who were hired to kill the Demon King, the hero party deserved their title as heroes as they saved the world from corruption and slavery.
Under the leadership of Alister, the hero party didn't care about racial differences and wasn't racist to other races. Undoubtedly, the reputation and fame of the hero party were well-known throughout Fantasia.
Even so, they still have forgotten about the Demon King!