This is an issue that was reported on the forums by the user and we resolved it on the forums. For completeness, here is a quote from the thread:
"In the case of the itemsSourceChanged, it doesn't get invoked because for you are setting the listView.itemsSource before registering the callback and the items source does not seem to change afterwards.
In the case of the itemsAdded callback, this is an event that is fired when items are added through the list view directly. In your example, you are manually creating items and adding them to the items source list. You would get the callback if you added items through the list view by using the showAddRemoveFooter for example.
One final note, you should be using OnEnable instead of Awaketo query to rootVisualElement from the UIDocument, as it is not guaranteed to be ready in the Awake call."