Maybe because Norwegian rats have some unique characteristics or behaviors that can make for an interesting story. They could add an element of mystery or adventure.
Writing about Norwegian rats in a short story can offer a fresh perspective. It could be used to explore themes like survival, adaptation, or the interaction between humans and these rodents. Also, their role in an urban environment might provide a rich setting.
One might choose to write a short story about Norwegian rats to draw attention to their often overlooked existence. It could be a way to humanize them or to create a cautionary tale. Plus, their social structures and behaviors can provide lots of story possibilities.