A lot of this comes from the very careful attention to detail that Square Enix put into designing the game’s art.
In a Game Informer feature, Square Enix talked about how every single thing they drew, they did while trying to sell it as a very real thing that exists in a very real world- for instance, when they were designing a building in Altissia, they modeled it after buildings in Venice, to sell it as a building in a real world, rather than as a fantastic construct.
You can check out the images below, and see for yourself whether or not Square Enix succeeded.
“We create a sense of size, scope and power by creating them in the likeness of real-life jumbo jets.”