Why was this show canceled before the story arc ended?

It was a somewhat better than average Saturday morning cartoon that wasn't afraid to explore themes of death, decay, and widespread destruction. The story line wasn't exactly original, but it had some nuanced twists. The villains were more appealingly loathsome than in most other shows. The overall quality of the scripts was good. Another season would probably have sufficed to wrap things up. Does anyone know whhy the network canceled it prematurely?