Human misery isn't something most companies want to be associated with. For that reason, many companies don't want their ads to run next to content like that. I've personally had to quickly pull ads off a site because of that fact.
http://www.niemanlab.org/2015/03/an-ad-blocker-for-tragedies...
If a story is marked as sensitive, an option is set and ads aren't shown on it.
The Guardian has this too. And I've done this on a few sites I've worked with as well.