Selective empathy is the culprit because it's based on conditioning and received values.  Prof. Singer puts the point admirably.

The question is whether we can help it and whether reason can help us overcome our biases. David Hume argued that reason plays no role in our ethical actions; only sentiment can motivate us.

Maybe we can expand our sentiments by questioning them. Why can't I stand suffering in dogs but am indifferent to chicken and fish?