Change combobox list based on option button

I have two buttons:

Private Sub Optionbutton1_Change()
Call UserForm_Initialize
End Sub

Private Sub Optionbutton2_Change()
Call UserForm_Initialize
End Sub

And code below:

Private Sub UserForm_Initialize()
Dim cPart As Range
Dim ws1 As Worksheet
Dim ws2 As Worksheet
Set ws1 = Worksheets("Sheet1")
Set ws2 = Worksheets("Sheet2")
Dim optbut As Integer

If Optionbutton2 Then 

        For Each cPart In ws1.Range("List1")
      With Me.CmbSiteName
        .AddItem cPart.Value
        .List(.ListCount - 1, 1) = cPart.Offset(0, 1).Value
      End With
    Next cPart


ElseIf Optionbutton1 Then

    For Each cPart In ws2.Range("List2")
      With Me.CmbSiteName
        .AddItem cPart.Value
        .List(.ListCount - 1, 1) = cPart.Offset(0, 1).Value
      End With
    Next cPart
    
End If

Me.CmbSiteName.SetFocus
End Sub

By default:
Optionbutton1=False
Optionbutton2=True

and 3 steps:

When I run User form - it's OK (looking at List 1)
When I click Optionbutton1 - it's OK (looking at list 2)
When I now click back to Optionbutton2 it remains at List 2.. Why doesn't switch to List1?