If you still haven't played Final Fantasy XV, and are super sensitive to spoilers, beware of what you're about to read, but as those of you who have played through the game know, it becomes a lot more linear during the second half of the game, something that has been receiving criticism.
Now the director Hajime Tabata has explained this decision in an interview where he says there simply wasn't any other choice:
"Based on calculations that the development time and cost would double if the latter half of the game was to be an open-world environment as well, we had already planned to make the latter half more of a journey by vehicle. The structure of this title - to create memories while traveling in the open-world environment during the first half of the game, then have the story move forward linearly using the train in the latter half of the game - was designed and intended to be that way."
We assume the debate whether this was the right decision or not will continue, but knowing that the game originally was announced eleven years ago, it's not difficult to understand why Square Enix wanted it released. Still, double the time and money for more open world seems at least slighty exaggerated, don't you think?