"Mankind called down your brothers and let them run rampant through the world. What more could they dare hope for but you?"
The final line is a kick in the pants, and it's supposed to be. I know a fair number of people wanted an ending that would imply a rebirth of sorts to the world, but this is the apocalypse! Humanity isn't bouncing back from this one, everyone.
Yeah, it's a bit bleak. But that's a fable for you - they don't always have happy endings, especially the cautionary kind. Yet you learn something from them, and maybe can make your own story a little happier from that knowledge, and avoid the terrible fate of those in the fable.
In our modern age, we absolutely have the tools and ability to put an end to famine, war, and pestilence (and climate change and poverty and more), but if we let our vices prevent us from using those tools and taking positive action, we will indeed bring about our own destruction and will wind up hoping for Death to end our plight.