In biology, there are always many causes, of course.

I wonder if people are familiar with the hypothesis of parasite-driven aging.

Parasites are vastly more prevalent than most people in modern, sanitary, medicated societies realize. Studies show that over half the biomass in a region may be parasitic.

Parasite frequently keep the host alive, but inhibit reproduction. This leaves the host alive, and competing with healthy members of its species for resources, but no capable longer reproducing. It's evolutionary dead weight.

Death is basically "turning it off and on again", just as you would do with a computer, and for very similar reasons. It clears the accumulated parasites and starts fresh.

This would also help explain why death is strongly conserved.