Multiline Regex Matching

[Empyreal]

I've been working with Regex and I've run into something that doesn't make sense to me; I either misunderstood how the Multiline option works, I'm not using it right, or it really just doesn't work like it's supposed to. This is a little test I made:

Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
    Dim TestString As String = "test" & vbNewLine & "sweet"
    Dim TestRegex As String = "^[a-z]*$"
    Dim ResultsString As String = String.Empty
    For Each StringMatch In System.Text.RegularExpressions.Regex.Matches(TestString, TestRegex, _
                                                                             System.Text.RegularExpressions.RegexOptions.Multiline)
        ResultsString &= StringMatch
    Next
 
    Console.WriteLine(resultsstring)
End Sub

The problem is, the only match that is found is the last line (in this case "sweet"). Why is this?