Why do all things that live have a limited time to do so? Why would nature or the universe impose that kind of restriction?
Birth without death would lead to overcrowding, but then why not evolve a mechanism to limit births? Surely a longer lived – or immortal – species would lead to positive growth, learning from your mistakes.
If evolution through DNA leads to positive changes, why not evolve a mechanism within to create those changes, slowly over time?
Why birth, and death? Why not just birth?