I think it's mainly because of how we feel about losing human lives vs animal lives. So it's emotion based. I think all other reasoning/justification comes after our emotions. Anyone can think of reasons that differentiate humans from animals, but ultimately it is just how we feel about it. And for emotions, yes this is for evolutionary reasons.

If we were to consider human lives equal with animal life we would have to change so much it would not be practical so at current state it is not even something ww would consider so many of us simply try to ignore the issue.