Why UI Events added scriptable in runtime not works before I disable-enable gameobjects or graphic object?

In play mode they not start working before I disable and again enable gameobject or graphic UI element. After that they working correctly.

I adding event scriptable something like this in Start() method:

 var eventTrigger = gameObject.GetComponent<UnityEngine.EventSystems.EventTrigger>();
         var eventTriggetDelegates = eventTrigger.delegates ?? (eventTrigger.delegates = new List<UnityEngine.EventSystems.EventTrigger.Entry>());
         var entry = new UnityEngine.EventSystems.EventTrigger.Entry();
         entry.eventID = UnityEngine.EventSystems.EventTriggerType.PointerDown;
         entry.callback.AddListener((eventData) => { UnityEngine.Debug.Log("UIElement PointerDown " + UnityEngine.Time.realtimeSinceStartup.ToString()); });
         eventTriggetDelegates.Add(entry);