I know we saw Egypt when Praimfaya(not sure if that's right) was first shown. It will feel really open world if there are other settlements in other places on earth and they also had their own struggles and issues and ways to escape the fallout. Clark's Eden is the only inhabitable place we've seen so far on earth (this is unlikely, it's far more plausible that there are other pockets of land too). Now the fact that for now, it is the only place that can support life could be a way to bring in other people on earth. Maybe not now, but after the prisoners story is done, they could open the world up.
This would have to be done very very carefully. It is a possibility but it would also be super easy to loose the premise of the show. With the focus on a single location they can detail the story more precisely and less chance of confusion with too large an area.
Jason said once he wanted to tell the story of people in other countries but that never happened so I don't know
Plus we already have Eligius 3 who is probably still somewhere in space so it's more likely we'll meet them than other people on Earth, especially if the theory saying that at the end of the Season the war will destroy Eden and they'll have to get to the cryo pods in space, I don't see how they would introduce other humans that survived on Earth...
Dystopia's usualy only follow a single location setting. Think hunger games, which was centered around Panem. No mention of the rest of the world was made, Up until the second season we hadn't seen much from outside the DC area. Now we've at least been introduced to other clans from all over the country (or at least the east coast).
Thing is that when the Ark formed, there were different nationalities. For English and subsequently an interest in US territory on earth to come out favorable for the delinquents mission is no surprise. Were there better drop-point options than mount weather, DC? Probably. Would they have been as interesting? probably not. The show decided to stick to this narrative, and they went back to their space-roots in S4 so I think that's the only expansion we will see in the world of The 100. S5's villains literally came from the sky and hadn't set foot on earth in a hundred years.