More like it's for pragmatic reasons and that SE just doesn't want to spoil aspects of the lore and story that is being kept in reserve for the future direction of the game - the cloud is clearly covering the entirety of Islabard apart from the spires of the Garlean capital poking up through the clouds ominously at the top of the map, so it's clear that the map will altered accordingly when the time comes (note also the Eorzean map is now updated to feature the Shalaryan colony actually designated as such (with the Shalaryan motherland above as 'Old Shalaryan'), and Ala Mhigo actually has it's flag and a proper graphic of it's appearance rather than a placeholder walled city that how the original Eorzea map depicted it as.)
Either that, or it's to hide parts of the map the lore team hasn't actually finalized ideas for yet, there is literally nothing there.