There were plenty of reasons that Walker could think of that would benefit them in bringing another species back to the world.
Part of it was that the world was changing. Plenty of plants were finally receiving the manas that they needed to grow properly. Other than that, bloodlines and ancient aspects of monsters were returning because they also had the environments and manas necessary to do so.
This meant that a monster like the Amorak might have a place in the food chains. Ensuring that certain monsters did not grow out of control. Or they would be food for a monster that needed a prey that could allow them enough nutrients and mana to grow.
However, Walker, Onyx, and Mordant focused on the fact that Amorak were a species of monster known to be more intelligent. They could have been intelligent enough to be able to eventually become a monster race recognized by the world.
