What else can I say
There are alot of animals that only mate periodically. Maybe penguins can't tell male from female unless they're in heat. Or maybe they evolved this behaviour to maximize the chances of chicks surviving in bitter cold antarctica. If one parent succumbs, another becomes a foster parent. Maybe all of the above. Maybe none of the above. Like I said, understanding the intricacies of social behaviours of distant species may not be possible for us. Humans do not necessarily behave the same way for the same reasons. We don't have the same physiology, or live in the same climate, eat the same food, respond to the same sensory inputs/outputs.