undo execute after macro

i have a macro to insert a new row and copy formula, from the row above
but if i do a mistake, the undo is not possible
why?

the macro is this one

Dim MyRow As Integer
MyRow = ActiveCell.Row
For Each Sheet In Sheets
    Sheet.Rows(MyRow).Insert
    Sheet.Rows(MyRow - 1).Copy
    Sheet.Rows(MyRow).PasteSpecial Paste:=xlPasteFormulas
    Sheet.Rows(MyRow).SpecialCells(xlCellTypeConstants).ClearContents
Next Sheet