c# TransactionScope没有回滚

我是c#新手，正在尝试TransactionScope是如何工作的。这是我的代码，我想知道为什么我的事务没有回滚:

string file1 = "txf1.txt";
string file2 = "txf2.txt";
using (StreamWriter sw = File.CreateText(file1))
{
    sw.WriteLine("Hello World");
}
using (StreamWriter sw = File.CreateText(file2))
{
    sw.WriteLine("Hello World");
}
using (TransactionScope scope = new TransactionScope())
{
    File.AppendAllText(file1, "Transaktion");
    scope.Complete();
}
using (TransactionScope scope = new TransactionScope())
{
    File.AppendAllText(file2, "Transaktion");
    //should roll back the file, but doesn't
}