Nature is cruel. Every living thing wants energy for itself, but there's only so much to go around. The leaves cry out in ultrasonic frequencies as they're harvested, and then we add insult to injury by drowning them in salad dressing before we chomp away blissfully. You want to live, just like they did. So you eat. If only the universe had infinite resources to go around, but instead the march of entropy leaves us fighting over an ever shrinking pie.

Yes, but for myself I'd rather eat things that aren't as smart as octopuses.

And as long as the sun keeps shining, the pie stays pretty constant on Earth. The pie is shrinking for everybody else only because humans keep taking more of it.