Why can not select all text in textbox after focus to textbox ?

Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load
       ListBox1.Items.Add("Times New Roman")
       ListBox1.Items.Add("Arial")
       ListBox1.Items.Add("Arial Narrow")
       ListBox1.Items.Add("Monotype corsiva")
       ListBox1.Items.Add("Verdana")
       ListBox1.Items.Add("Andelip")
       ListBox1.Items.Add("Obit BT")
       ListBox1.Items.Add("LCD")
       ListBox1.Items.Add("Western")
       ListBox1.Items.Add("Roman")

       ListBox1.SelectedIndex = 1
       TextBox1.Text = ListBox1.SelectedItem.ToString

   End Sub

   Private Sub TextBox1_KeyDown(sender As Object, e As KeyEventArgs) Handles TextBox1.KeyDown
       If e.KeyCode = Keys.Down Then
           If ListBox1.SelectedIndex <= ListBox1.Items.Count - 2 Then
               ListBox1.SelectedIndex = ListBox1.SelectedIndex + 1
               TextBox1.Text = ListBox1.SelectedItem.ToString

               ListBox1.Focus()
           End If
       End If

       If e.KeyCode = Keys.Up Then
           If ListBox1.SelectedIndex >= 1 Then
               ListBox1.SelectedIndex = ListBox1.SelectedIndex - 1
               TextBox1.Text = ListBox1.SelectedItem.ToString

               ListBox1.Focus()
           End If
       End If
   End Sub

   Private Sub ListBox1_GotFocus(sender As Object, e As EventArgs) Handles ListBox1.GotFocus
       TextBox1.SelectAll()
       TextBox1.Focus()
   End Sub