Why is nature so brutal, violent, and chaotic?

I am curious because animals cannot sin or do things that are evil in an ethical sense. But it's pretty clear that reproduction is the only thing that matters in nature. Lions eating their own cubs is not evil, it's just a way to maximize the chances of their genes being passed down.

But why is infanticide a part of nature anyway? Why are animals suffering like this, especially since their suffering has no chance of being sanctified according to theologians like Aquinas?

I have heard a Christian suggest that animals live in perfect harmony with God, as they cannot sin. I find this idea a bit unsettling when soberly looked at.