Why doesn't ListView.ScrollIntoView ever work?

I am trying to scroll into view so that the very last item in a vertical listivew is always showing, but ListView.ScrollIntoView() never works.

I have tried:

button1_Click(object sender, EventArgs e)
{
   
            activities.Add(new Activities()
            {
                Time = DateTime.Now,
                Message = message
            });

            ActivityList.ItemsSource = activities;
            
            // Go to bottom of ListView.
            ActivityList.SelectedIndex = ActivityList.Items.Count;
            ActivityList.ScrollIntoView(ActivityList.SelectedIndex);
}

I have also tried:

ActivityList.ScrollIntoView(ActivityList.Items.Count), and ActivityList.ScrollIntoView(ActivityList.Items.Count + 1); but nothing is working.

The documentation isn't very helpful in this case.