为什么不能用Abort退出线程

class threadAbort
    {
        static void Main(string[] args)
        {
            WriteMessage(\"主线程开始工作\", ConsoleColor.White, ConsoleColor.White);
            Thread th = new Thread(new ThreadStart(TestTry));
            th.Start();
            Thread.Sleep(500);//500毫秒后结束线程
            th.Abort();
            th.Join();
            WriteMessage(\"主线程结束工作\" + th.ThreadState.ToString(), ConsoleColor.White, ConsoleColor.White);

            Console.ReadKey();
        }

        private static void TestTry()
        {
            try
            {
                for (int i = 0; i < 10; i++)
                {
                    WriteMessage(\"线程正在工作中\"+i.ToString(), ConsoleColor.Green, ConsoleColor.White);
                    Thread.Sleep(100);
                }
            }
            catch (ThreadAbortException ex)
            {
                WriteMessage(\"线程错误信息：\" + ex.Message, ConsoleColor.Red, ConsoleColor.White);
            }
            finally
            {
                WriteMessage(\"线程退出。。\", ConsoleColor.Blue, ConsoleColor.White);
            }

            //如果线程未结束，直接Abort线程，下面语句将不会被执行。
            WriteMessage(\"线程结束工作.\", ConsoleColor.Yellow, ConsoleColor.White);
        }

        public static void WriteMessage(string message, ConsoleColor writeColor, ConsoleColor backColor)
        {
            Console.ForegroundColor = writeColor;
            Console.WriteLine(message);
            //Console.BackgroundColor = backColor;
        }
    }