Because there's no pleasure in that for humans? Of course that becomes wrong if many humans embrace the idea that minimizing suffering for animals is a good th

Because there's no pleasure in that for humans? Of course that becomes wrong if many humans embrace the idea that minimizing suffering for animals is a good thing. At that point you would also be increasing the humans' "moral/ethical pleasure" in a kind of self fulfilling way. But there's no reason for this to happen except human hubris.