Death & Disease

Beyond doubt Death and Disease are the biggest ones. Why should these be? We will focus not on the process (we know death happens due to the failure of organs due to natural or non-natural reasons but that is not the basic issue) but on the underlying basic issue, the raison-de-aitre rather than the appearance. Why are our bodies so fragile? Why do our cells age? Will this change? If so, how? Have we made peace with death? Should we not question it? What about diseases? Why are our systems (vital,mental,physical) so fragile so as to not to be able to resist shocks around us? Why should there be diseases?