This is the closest to a complete map as we'll see for the the time being


But yeah, as other's have said realistically the devs just have not planned that far in yet and would like room to make additions once they get to that point. But when it comes to in-game lore then I'd imagine the Garleans have a rough map of the lands they've occupied + the Eorzean map. Most likely the Allagans have a complete world map since they conquered it all.