User blog comment:ImperiexSeed/The oldest being, archangel or leviathan?/@comment-24.255.23.122-20120507204417/@comment-4920092-20120507205112

They aren't curing Humans because the diseases can hurt them, their curing humans to increase net product. It's the same reason we cure cows - most of their diseases aren't communicable across species, but we want more cows to live, so we can eat more of them.

In the same way, if humans are dying off because of disease, they won't be able to eat as many of us.