1) They'd need enough of you all to help. Building a world from scratch will mean it won't have the same kind of limitations that come from building one from memory, but they'll need to crowdsource that creativity.

2) It'd be significantly smaller. Like, one of the bigger islands in size. One of the reasons the archipelago couldn't last is because there were too many elements and the Storyteller was stretched too thin.

3) There would not be a guarantee that they'd be able to send everybody home (or to wherever they needed to go) after constructing something like that. They could try doing it before constructing it, but then they run the risk of not having all the creativity needed for point one. Granted, it might be possible to make that new world capable of travel to an extent so they could try and get people to where they need to go manually, but that would take longer.

4) If this option was picked, the Storyteller would need to stay behind and maintain this world. They wouldn't be able to go back home with anyone else. (For their part, they're willing to make this sacrifice.)