The receding rot and the fact that the tree itself is looking healthier the more the Watering Can pours makes the pixies look forward to the changes happening on it. Elaina did not stop to pour water on the spots of corruption, making sure each of them slowly disappears.
The process was slow but it is working miraculously which is what Elaina wanted. Even the pixies around were not expecting the healing process of the corruption as well. If they have known a tool like what Elaina is carrying could actually remove the one making the World Tree rot, they would have focused on finding it just to ensure the tree would have not progressed into the worst state it would have been.
