Frustration Or Shame.

This beast is like an ant lion in its sand pit. But unlike an ant lion, it is not passive in its hunting. The 10 tails of the beast reach out of the pit to drag in careless vampires. This is despite being surrounded by thousands of Vampires who are attacking it from every direction.

The Vampires are not weak either. Each one is equal to an Origin god that has reached the limit of the void universe, so they are very powerful. Each of their attacks shreds a part of the pit. 

The Vampires are not useless. Their attacks are the major reason why the bottomless pit is not bigger. They chip away at it little by little. But all their attacks cannot destroy it because this beast appears to be endless. It is always growing as it devours the world. 

There is a sphere of gravitational pull around the beast that is affecting everything around it. Matter and energy are pulled to the beast, where they are devoured. This is what is fueling its constant growth.