there's a few complexities. first, the intent of the app is primarily to be a bluetooth / wifi mesh, and many people won't use nostr at all. second, it makes a new key for every "channel", and even if you don't override your location (teleport) you make a new key for every level that you post in. third, it rotates keys sometimes - i'm not sure how often. so, there should be many more pubkeys than bitchat/nostr users