This section is narrated in the second person, addressing “you,” who the narrator says should be noticing certain things missing. For example, no one in this world speaks of islands or other continents besides the Stillness. Similarly, no one pays attention to stars or celestial objects, instead focusing only on the earth. Because of this, they do not notice “what’s missing” in the sky, as it is something they have never imagined was supposed to be there. So, the narrator says it’s fortunate that “there are more people in this world than just humankind.”
This “you” is presumably still Essun, but it also seems directed to the reader who is still being introduced to this foreign world. Just as the people of the Stillness ignore the obelisks and ruins of ancient civilizations, they’ve also learned not to pay attention to the sky at all, or to lands besides their own. The line about something “missing” in the sky is an early hint that the moon will play a role in the story in the future. The other people besides humans might be stone eaters, who remain mysteries at the edge of the narrative for now.