What’s the bigger picture for animal suffering in Islam?

Assalamu alaikum, folks. So we know Islam tells us to be kind and fair to animals-the Quran and hadith are clear on that, no question. But something has been bugging me. Nature itself is pretty harsh, like that whole wasp and caterpillar thing Darwin talked about. And after animals die, it seems like they’re just gone, turned to nothing. Here’s where I get stuck: why would animals suffer their whole lives if there's no reward or point? We humans are tested, right, but animals aren’t. So what’s the reason for their pain? I can't make sense of it.