Besides the sensible meta-reasons explained by Moose, and the Calamitous re-geography-ing explained by Razor, we should also consider that maps (as would have been accurate during Allagan reign) quite probably do exist, but they are in non-paper (tomestone) format or otherwise very well hidden. Five thousand years is a long time for paper records, and they are not likely to have survived unless kept in sealed, magicked, or otherwise protected locations.
To draw a real-world parallel, we Earthans have shifted a great amount of our record-keeping to electronic formats in the last few decades, and books from even just a few hundred years ago might require careful preservation and handling to keep them from crumbling on contact.