To me, the answer is that pain down here is of no concern at all to the beings above this level. They can take no sadistic pleasure in it because it is irrelevant to them -- it is like a story from a distant land. Even for the animal in question it is unpleasant and maybe unbearable, but it is relevant only in the moment, and once it passes or the animal dies, it has no further influence. It is a purely local effect. Even in our own lifetimes the periods of injury or pain become just memories soon after. They may continue to have influence only through traumatic associations, but in that case it is not pain which is the problem but rather emotion.

As I watch my baby son go through teething pains, I wonder why our existence is so uncomfortable right from the start. From a Darwinian perspective, the mechanism works, the pain is irrelevant. From a spiritual perspective, you can take the approach that the pain is a chance for the being to improve its qualities. Whether that is the 'right' answer or not, it is a pragmatic way to make use of an unpleasant stimulus.

I well remember physical training classes as a child, and it made me wonder about the nature of time, why it was 'now' that I was experiencing the pain (I suffered from stitch), and why 'now' was not 'later', i.e. why my experience was so tightly focussed on just one point on the timeline of my life, the one where I was experiencing pain. I still don't have an answer to my question about the nature of our experience of time.