Unity 2D Game Issue: Script is only affecting one prefab instead of all of them.

I have a problem in a game that I'm making. I have a script attached to a prefab that is supposed to make every instance of the prefab spawn at the top of the screen once it hits the bottom of the floor.

 #pragma strict
 
 function Start () {
 
 };
 
 function Update () {
     
 };
 
 
 function SpawnLoop()
 {
 gameObject.SetActive (false);
 yield WaitForSeconds (Random.Range(0.0,5.0));
 gameObject.SetActive (true);
 transform.position = Vector2(transform.position.x,6);
 };

Why is this only affecting one instance of the prefab instead of all of them?