Why is a FOR of the loop faster than 10 FOR together

I made a for alone count to 1000000 (sending 1 message to each loop ) and it took 14 seconds.

public class main 
{
public static void main(String[] args) throws InterruptedException
{
    long init  = System.currentTimeMillis(); 

    Thread ataque = ataque();
    ataque.start();
    ataque.join();

    long end  = System.currentTimeMillis(); 
    long diff = end - init;
    System.out.println("Demorou " + (diff / 1000) + " segundos");
}

static int limite = 1000000;
static int for1 = 0;
static int for2 = (limite / 10);
static int for3 = for2 + for2; 
static int for4 = for3 + for2; 
static int for5 = for4 + for2; 
static int for6 = for5 + for2;
static int for7 = for6 + for2;
static int for8 = for7 + for2;
static int for9 = for8 + for2;

public static Thread ataque()
{
    Thread t = new Thread() 
    { 
        @Override 
        public void run() 
        {
            for(int i = 0; i <= limite; i++)
            {   
                System.out.println(i + " de " + limite); 
            }
        }
    };
    return t;
}
}

Soon after I split these for into 10 different ones by simultaneously executing 10000000 (sending 1 message every loop ), it took 15 seconds.

public class main 
{
public static void main(String[] args) throws InterruptedException
{
    long init  = System.currentTimeMillis(); 
    Thread t1 = ataque1();
    Thread t2 = ataque2();
    Thread t3 = ataque3();
    Thread t4 = ataque4();
    Thread t5 = ataque5();
    Thread t6 = ataque6();
    Thread t7 = ataque7();
    Thread t8 = ataque8();
    Thread t9 = ataque9();
    t1.start();
    t2.start();
    t3.start();
    t4.start();
    t5.start();
    t6.start();
    t7.start();
    t8.start();
    t9.start();
    t1.join();
    t2.join();
    t3.join();
    t4.join();
    t5.join();
    t6.join();
    t7.join();
    t8.join();
    t9.join();

    long end  = System.currentTimeMillis(); 
    long diff = end - init;
    System.out.println("Demorou " + (diff / 1000) + " segundos");
}

static int limite = 1000000;
static int for1 = 0;
static int for2 = (limite / 10);
static int for3 = for2 + for2; 
static int for4 = for3 + for2; 
static int for5 = for4 + for2; 
static int for6 = for5 + for2;
static int for7 = for6 + for2;
static int for8 = for7 + for2;
static int for9 = for8 + for2;

public static Thread ataque1()
{
    Thread t = new Thread() 
    { 
        @Override 
        public void run() 
        {
            for(int i = for1 ; i < for2; i++)
            {
                System.out.println(i + " de " + limite); 
            }
        }
    };
    return t;
}
public static Thread ataque2()
{
    Thread t = new Thread() 
    { 
        @Override 
        public void run() 
        {   
            for(int i = for2; i < for3; i++)
            {
                System.out.println(i + " de " + limite); 
            }
        }
    };
    return t;

}
public static Thread ataque3()
{
    Thread t = new Thread() 
    { 
        @Override 
        public void run() 
        {
            for(int i = for3; i < for4; i++)
            {
                System.out.println(i + " de " + limite); 
            }
        }
    };
    return t;
}
public static Thread ataque4()
{
    Thread t = new Thread() 
    { 
        @Override 
        public void run() 
        {
            for(int i = for4; i <= for5; i++)
            {   
                System.out.println(i + " de " + limite); 
            }
        }
    };
    return t;
}
public static Thread ataque5()
{
    Thread t = new Thread() 
    { 
        @Override 
        public void run() 
        {
            for(int i = for5; i < for6; i++)
            {
                System.out.println(i + " de " + limite); 
            }
        }
    };
    return t;
}
public static Thread ataque6()
{
    Thread t = new Thread() 
    { 
        @Override 
        public void run() 
        {
            for(int i = for6; i < for7; i++)
            {
                System.out.println(i + " de " + limite); 
            }
        }
    };
    return t;
}
public static Thread ataque7()
{
    Thread t = new Thread() 
    { 
        @Override 
        public void run() 
        {
            for(int i = for7; i < for8; i++)
            {
                System.out.println(i + " de " + limite); 
            }
        }
    };
    return t;
}
public static Thread ataque8()
{
    Thread t = new Thread() 
    { 
        @Override 
        public void run() 
        {
            for(int i = for8; i < for9; i++)
            {
                System.out.println(i + " de " + limite); 
            }
        }
    };
    return t;
}
public static Thread ataque9()
{
    Thread t = new Thread() 
    { 
        @Override 
        public void run() 
        {
            for(int i = for9; i < limite; i++)
            {
                System.out.println(i + " de " + limite); 
            }
        }
    };
    return t;
}
}

Why is he even "10 times more efficient" still giving a worse result?