Another Physics.OverlapSphere question

When I check to see the hitColliders.Length it says that the size is 0. Why isn't my array filling up?

 void Update () {
         if (Input.GetMouseButtonDown(0)) {
             if (iu.brush) {
                 Sweep();
             }
         }
      }
 void Sweep() {
         Vector3 mousePosition = new Vector3(Input.mousePosition.x, Input.mousePosition.y, camDist);
         Vector3 objPosition = Camera.main.ScreenToWorldPoint(mousePosition);
 
         Collider[] hitColliders = Physics.OverlapSphere(objPosition, 5f);
         Debug.Log(hitColliders.Length);
         foreach (Collider col in hitColliders) {
             if (col.gameObject.tag == "BrokenAcorn") {
                 col.GetComponent<Rigidbody2D>().AddForce(new Vector2(1000, 200));
             }
         }        
     }