Suffering could just be a consequence of having an organic body that fails. Without pain- we may not realise that we have a cut that has become infected. So- pain prompts us to try and heal ourselves. In some ways, I suppose pain is there to stop the situation getting worse. If you eat something dangerous, you'll likely get a stomach pain and throw up- otherwise, you'd eat more of it. The problem of course, is that we can't always heal our injuries and illnesses but I suppose the pain signals we get can't be turned off consciously.
As for- why do we inflict suffering on others? I guess to some extent, predators are given a desire to hunt and kill and eat things in order to survive. We'll also exploit our environment in order to survive. I'd say most animals are actually trying to compete for dominance. It's just that they are better kept in check than we are.
The whole concept of pain and suffering as evil though is a criticism we've placed on it. It's just that humans appear to have a greater capacity to be able to look at this world and make judgements about it. We also feel wronged by it and bitter about it. I'm not convinced that other animals do this.
If a wilderbeast narrowly escapes with it's life but has one leg torn off by a pack of lions, I don't think it necessarily resents or hates the lion. It definitely fears it- understandably. Still- you don't get the impression that animals question why they have had so much bad luck. They either just get back on with trying to survive or, they give up and die. We can't know for sure but surely- if they thought like us then- we'd surely see more animal suicides in the wild. Who wouldn't feel depressed and suicidal being a wild animal?!! Not enough food, your home being destroyed or polluted, your family and yourself being hunted and killed.
Really- it comes down to whether you believe there was intention behind this- an original creator or God- in which case- it seems fair to ask what the hell they think they're doing. If it all just happened via unconscious forces like gravity, chemical reactions, evolution though- then- we ended up this way because it enabled us to be the dominant species. I doubt there would be intention behind that. It just happened that a living being with a superior sense of it's surroundings and how it interacted with them was smart enough to stay alive longer in order to reproduce. Pain and a fear of pain would likely enhance that.
Perhaps being so accutely aware of suffering means we do all we can to avoid it. Health and safety protocols would seem to fit that. Ultimately as animals- the goal is survival and reproduction. We've become far too good at that in fact. So- as awful as it may seem to us, pain and suffering are inconsequential to that to an extent.
Of course- many of us here though are breaking nature's rules. Many people here are anti-natilists and we obviously want to end our lives early. That has largely come about via pain and suffering I imagine- so- as a tool to keep us alive- if that's what it started out as, it's starting to backfire I suppose. Not that it will make a difference I suspect. There are already more than enough of us I imagine to cause catastrophic changes to the climate- then- we're all f*cked.