why buoyancy effector 2d dont work in a sprite shape in unity code example

Example: unity buoncy changing

void Start()
    {
      StartCoroutine("coRoutineTest", 1f);   
    }


IEnumerator coRoutineTest (float waitTIme)
    {
        while (true)
        {
            

            buoyancy.surfaceLevel = Random.Range(4f, 2f);

            yield return new WaitForSeconds(waitTIme);
        }
    }