The same question was asked here: Why are there no maps of lands east of Westeros in The Game of Thrones? but the answers were focused on what reasons GRRM hadn't mapped it. I'm interested in what reasons people of Essos might have not yet have mapped the area?
For example, about Sothoryos is said this:
"covered in jungles, plague-ridden, and largely unexplored. The northern coast has been mapped, with the ruined cities of Zamettar, Yeen, Gogossos and Gorosh noted, but little else is known of them. Explorers of the Summer Isles may have mapped southern Sothoryos. If so, they keep these maps a close guarded secret. Besides the savage Brindled Men, particularly the ghouls and cannibals from the deep jungles, Sothorys is home to many fatal diseases, including blood boils, green fever, dancing plague, sweetrot, bronze pate, the Red Death, greyscale, brownleg, wormbone, sailor's bane, pus-eye, and yellowgum."
Those are understandable reasons. But why is east of Essos unknown? From this map you can see that just before the map ends, there is Grey Waste, which is "an expansive, cold desert" and possibly hard to cross.
But in the map there are elements that don't support the idea that the eastern part is hard to reach. For example there are two cities right before the map ends, City of the Winged Man and Carcosa. Both are said to be "legendary", but Carcosa seems to be a living city, and "is ruled by a sorceror lord claiming to be the 69th yellow emperor of Yi Ti." Also from Nefer to east there is a forest area Mussovy.
Taking all this information into account, it doesn't seem likely that people don't travel to east and it doesn't provide reason why map ends so abruptly. What might be the reason?