The Evolution of Man
Excellent question. And before I explain the real answer, which is rather mind-bending, here are some previous arguments and why they are wrong.
Myth 1: We die to make room for younger generations.
Genes are selfish, and each individual body is a vehicle for a collection of genes. These genes are selected to favor the survival of copies of themselves. Since parents and offspring use the same resources, the death of a parent creates room ecologically for just one offspring.
Source: According to the theory of evolution, why do we die?
My Comments: Very interesting piece from Quora!