So many random words to say about this, so bare with me here.
-While the location of importance is Europe, and Asia just happens to travel there from time to time, I think of the whole events in Soul Calibur to be a worldly thing. For example, the Evil Seed event. However, since this game was so focused on Patroklos and Pyrrha, that can explain why other continents are not included, and as to why Asia's portrayal is soooooooooo small. That could also explain why Talim and the Koreans aren't there, unless they all have ships to travel.
-Personally, the most unique you could get out of an American is a Native American at best, and Bangoo would fit the bill. A slave wouldn't be as pleasing (which is why I liked the African Tribal approach, or Zasalamel, instead, even though his physical body is from Africa, and not "Zasalamel" himself), while a Caucasian......we have too much of those already.
-While Eurasia was serving an important part of the plot, what about Persia, or Arabic characters? A little off topic, but they are a part of Eurasia.
But to sum it up, it's probably the whole setting in this game. Hopefully they do have a more international roster in the next game, but until then, we can just take what we have.