I thought about this too. The explanation I've reached is that when it comes to livestock, there is a certain amount of.. respect? going into the process. We are raising and exploiting cattle for thousands of years now, and every part of an animal is either directly consumed or used in other ways. Many cultures have elaborate rituals surrounding the slaughter, etc. This, I think, gives the impression of value to us.

But for these penguins, there is no respect (still not sure if this is the best word) to speak of. You just cut them into pieces and boil thousands of them in a steampot, then discard most of it. The oil you get is in small quantities and is not even of high quality. The animal is treated as a thing to be used up, without any value.