Probably a lot of elephants die to infections because they don't have antibiotics, or famine or poaching or the flu or a lot of other causes that we reduced.
It's so high because we eradicated so many other things that used to kill us off early.
Looking at the leading causes of death in the UK[1] they're: dementia, heart disease, strokes, lung cancer, flu. If you lowered any of those then the rates of the others would go up.