User blog comment:Zathronas/Analysis by an author: Volume 2 episode 9: Search and Destroy/@comment-5217560-20141003033732/@comment-24218038-20141003130529

That's the most probable answer but I'm gonna go in another direction.

Remember what Oobleck said about the lone Beowulf? It can sense ill intent, they are attracted to negativity. Fear, sadness, envy, loneliness and hatred attracts the Grimm.

What happens when a whole kingdom feels that way?