The puzzle of aging is less how it happens, given that the scientific community has a good catalog of the forms of cell and tissue damage that cause aging, and can work to prove relevance by repairing that damage, but rather why it happens. Serious attempts to intervene in the aging process have long been a minority concern when compared to the funding and careers devoted to explaining the existence of aging. Understanding why evolution has led to a world dominated by species that age, alongside a tiny number of species that do not, is a thorny problem.
This is in part the case because arguments over the evolution of aging proceed by thought experiment and modeling rather than by examination of data. There is the world as it exists today, a few slim hints about the past, and researchers must deduce how this fantastically complex array of systems came into being over hundreds of millions of years from the minuscule sliver of information provided. There is a great deal of room in which to be wrong.