Erina is a world of elements and Elementals. Elementals, who have a habit of not getting along very well. Peace is temporary around here, and it's just best not to get used to it. Never know when the Fires are going to start another surprise world war...
At the end of the day, the world of the Elements is a world ruled by chaos and magic. With the universe not even playing by the rules it probably should be listening to, and people able to alter reality just by snapping their fingers.
Because what fun is there in making sense?