Norse Mythology Locations in Dominion Antarctica

I noticed that a lot of the locations in the Dominion Antarctica map are named after fictional locations or landmarks in Norse mythology, including:

• River Gjöll
• Hel
• Éljúðnir
• Valhalla
• Yggdrasil
• Þrúðvangr
• Niflhel
• And maybe some more I missed.

Why were they named after fictional locations instead of real-life locations and landmarks in Antarctica?