All the quest locations/quests themselves/monster locations/ect would have to be changed, and that's a TON of work to even attempt. They originally made the 2.X areas smaller because of how ginormous the 1.X areas were, and you didn't even have different regions in those maps, just winding path after path after path.

We're trying to prevent things from happening to Eorzea. We still have a lot more to explore in it. And it's normal for older areas in MMOs to be sub-par when comparing to new areas, so there's no real reason besides 'people are bored with it', as your post is coming off to me. Not saying you're saying these words, but that's how I'm seeing this.