Why are sumatran elephants cirtically endangered?

Because of Hunting. Elephants are probably the largest living mammals on earth. They don't have any natural predators that can attack a full grown elephant. However, lions and packs of hyenas have been known to attack an injured or extremely old elephant or an elephant calf that has strayed away from its herd. Humans are the biggest enemies to elephants. Armed with guns hunters and poachers are the biggest threat to elephant numbers.