because at some point in time, there (someone claims) was a dragon who ate people and made life hard, there had to be someone to rise and put a stop to this source of suffering and called it evil.
and because it was evil, its opposite was good. That opposite being the death, the non-existence, the change of the order of things that caused suffering
but the suffering did not end, only the dragon ended. That which can be pointed and run from, that which exists in a space and a time and a situation and has a name
but the suffering from being afraid of being eaten also stops when the dragon is left alone. So the question, why did the hero go to the dragon?
there is no reason for the hero to want a dragon, it is the existence of a dragon that necessitates the hero. only the hero has the capacity to become a hero when there is a dragon to defeat, without a kind of dragon, there is no kind of hero.
only that the fact of death, suffering, of houses burning and wifes dying, of children orphaned and the old people alone in cold nights did not go away. The only thing that went away was that thing that can be pointed at and ran away from.
the hero did not need to go to the dragon, the dragon did not need to do evil deeds, and the village did not need to fear the dragon. These things just happened with no reason, one thing was there then the other. There was no cause for it, there was no need for the situation to be in this way.
what did the dragon want? what did the village want? they just want a full stomach, to avoid being cold, to satisfy whatever they felt like.
maybe the human who saw the dragon and called it evil, could just the same point to the neighbor town and call it evil. And the hero then goes to the neighbor town and defeats them and is called a hero.
but the dragon and the village and the hero and the neighbor just happened to be there, for whichever reason, for whatever purpose.
without things to defeat and heros to fight, theres nothing that can happen and no story to tell.
the reason why the hero is even thought of, is that a dragon is necessary, without which, the hero is just another villager who had to suffer just like any other suffering, with no purpose by deeds and no name to remember.