http://boutcheetah.zylongaming.com/index.php?topic=50697.0A better question to ask would be why have the mobs not moved at all? As in the same position in which they spawn.
Plus there is the fact in the ss you can see the timer of 6 seconds into the game, yet the lv 180, nubby armor non-transed, apparently killed at least 1 mob (as seen from the explosion wave,) as well as getting rid of the 3 mobs that came before it.
Going by the explosion wave of the killed mob, and the sight range of the Scalper and Slammer (as in range that the mobs will see you and attack you,) is rather odd that they are standing calmly in their exact spawn location.