As much as I love overworld maps, they're probably too expensive to produce in modern games. The last JRPG I remember with a traditional overworld map was Tales of Vesperia, and Final Fantasy hasn't had one since IX.
Then there's the question of how they'd restrict access to areas not yet developed... yeah, I'd like an overworld map and airship, but it's just not practical these days, in this type of game.