Board Thread:New Chapter/Episode Discussion/@comment-5916303-20161222112427/@comment-5916303-20161224034904

There actually is some at the beginning. Aria's father explained the Empire's foreign relations to Tatsumi, Esdeath frequently spoke about the country's geography and terrain and Najenda occasionally delivered historical events to Night Raid.

I'd say it's the writer's choice, some do have last names like Seryu Ubiquitous, Numa Seika and Babara Oarburgh, however, in real life, there are cultures that sustain from having last names, particularity somewhere in Indonesia.