Steve,
How do the forces of nature and animals sin? I don’t see the problem if the forces of nature and animals don’t sin. They are not moral creatures. Nature doesn’t sin and therefore there is no natural evil.
As for reasons. Nature provided for humanity’s quality of life and civilization through millions of years of death and decay. Multiple generations of plant and animal death enriched earth with vast biodeposits, e.g., top soil, coal, oil, gas, limestone, marble, and concentrated metal ores. Nature produced the resources we need to fulfill the Great Commission, to spread the good news worldwide. As for present reasons. We will have to wait until the future to see how the present death, suffering, and decay benefits us. We can see some of the past reasons, so, I have confidence that we will see in the future some of the reasons for our present state when it is revealed.