It doesn't help that there's no real sense of technological progression. We started this game in essentially the middle ages and then thesteamceruleumpunk empire was cutting edge, and then the sci-fi empire that fell 5000 years ago started having relics awoken and now thesteamwaityessteampunk goblins are building on Garlean and Sharlayan scraps while Cid builds on Garlean and Allagan scraps and so on and so on. It's such a hodgepodge that you can't say what tech or references should exist here and now.
Yet... You have to figure Allag had a pretty nice map of the world by the end considering spaceships and satellites. You have to figure Garleans have some pretty nice maps of Ilsabard and Othard, considering they conquered them. Jalzahn probably has a map of Thavnair on him. So why is nobody communicating and corroborating and making any joint effort?
On one hand, as Enkidoh said, the team is better off not making any commitments that can't be modified and polished a bit as that content comes out. They know at least the rough idea; hell, we know the rough idea. We just don't know latitudes and coastlines, which will be fleshed out more as region maps are made for where ever we head next.
On the other hand, though, it also kinda messes with the spirit of the world lore a bit to release the full maps too soon. Lewphon of Sharlayan made our calendar 1344 years ago. Allag was a myth until ~550 years out. The map of our own home continent wasn't completed (as far as anyone living here now is concerned) until 71 years ago. And these are all allegedly huge achievements. Until the time is right, it's kind of anticlimactic for them to load up a tomestone and borrow some foreigners' maps and be like "PRESTO! There it is! Marvelous, isn't it? Alright, nobody's gonna need that for a few years, so I'll keep it. Off to Ala Mhigo with you!"
A map arrives precisely when it means to.