I think SE has basically admitted that in its current state the game is not what anyone can call "finished" and so the priority is to get everything working at an acceptable level before they add more to the main stories.

As you say, the story is what draws people to FF as a series. But I think the priority right now is to make sure that everything else works well enough that people are willing to play the storylines. Once everything is working they will have years and years to add story, or atleast that's the hope.

It helps to think of it as still being in beta for now. Storylines don't need beta testing, battle systems, UI, monster interaction all need to be in working order, then the story can be expanded.