Почему interrupt в main не прерывает работу нити?

package com.javarush.task.task16.task1617;

/*
Отсчет на гонках
*/

public class Solution {
    public static volatile int numSeconds = 3;

    public static void main(String[] args) throws InterruptedException {
        RacingClock clock = new RacingClock();
        Thread.sleep(3500);
        clock.interrupt();
    }

    public static class RacingClock extends Thread {
        public RacingClock() {
            start();
        }

        public void run() {
            Thread current = Thread.currentThread();

            while (!current.isInterrupted()) {
                if (numSeconds == 0) {
                    System.out.print("Марш!");
                    break;
                }
                if (current.isInterrupted()) {
                    System.out.print("Прервано!");
                }
                try {
                    Thread.sleep(1000);
                } catch (InterruptedException e) {}
                System.out.print(numSeconds + " ");
                numSeconds--;
            }
        }
    }
}