I think a surprising amount of writers don’t realize that tragedies are supposed to be cathartic. They’re intended to result in a purging of emotion, a luxurious cry; the sorrow caused by a great tragedy is akin to fear caused by a good horror movie – it’s a “safe” sorrow, one that is actually satisfying to the audience. It can still be beautiful! It’s isn’t supposed to just be salting the earth so nothing can grow.
But that’s how you get grimdark: writers who don’t realize that they’re supposed to be doing something with the audience instead of to the audience.