Biology has two purposes. One is the continuation of species, that is, the continuation of its own genetic material. Second, the expansion of population and territory has further spread their genetic material. This is also the instinct of biological survival.
You only see the first purpose of reproduction, but not the second purpose.
Even if human beings can live forever, they will continue to reproduce. At this time, reproduction is not only for the continuation of genetic material, but also for the expansion of population, so that human beings can use a larger number to spread to farther places and let their genetic material occupy a broader space.