I am still of the mindset that most (if not all) of the worlds' second visits were late-in-development decisions.
True worlds like Olympus Coliseum and Beast's Castle continue their plots in their second visits, and there is reason for you to come back later to finish the story.
But for other worlds their second visit plots just feel like they were created last second to warrant a second visit to me. Having very little to do to tie them in with their first visit plots.
I'm not sure I can describe what I mean properly but I shall give it a try.
Let's take Halloween Town, for instance:
In the first visit Jack wants to handle all the christmas stuff, so he has a santa outfit made for him, which he dons at the end of the visit. Maleficent is present because...Idk, she is a villain so she has to be present in the game somehow, and inbetween world-cutscenes are so KHI, KHII is too mainstream to need them. Anyway she revives Oogie Boogie, they kidnap Father Christmas, re-decorate his workshop, Sora & co fight Oogie, the day is saved and Jack learns to leave Christmas to the pros. Oh and we have a small visit with dr. Finkelstein, who has been working on an experiment.
In the second visit Finkelstein's experiment has disappeared, and someone is stealing presents from Christmas Town. Jack is still wearing his Santa outfit, much to the dismay of those around him, but really the tie-ins to the first visit end there. Jack is wearing the Santa outfit Sally made for him and dr. Finkelstein's missing experiment which had like two seconds of cameo screen time is a driving force now. I'm sure the present stealing plot was added to give a reason to return to Christmas Town the second time around, but really that just makes it so we have no reason to return to Halloween Town. In fact I tend to forget to enter Finkelstein's Lab during the second visit so I don't have a save point in Halloween Town when needing to grind for synthesis.
Or if we take Agrabah, in the first visit we have to prevent someone (Pete) from releasing Jafar from the Lamp, and we hide it away in a tomb.
The second visit litterally starts with Jafar being released, making all of the first visit pointless. How did the Peddler even get inside that tomb? I always presumed it was part of the Palace's dungeon, and what fumbling guard would let him inside the Palace in the first place?
In Pride Lands the villain pestering Simba is the exact same villain we killed in the first visit. I know that Scar's ghost's presence hs to do with Simba's self-doubt, but was there really no other possible choice of villain? Pete was present in the first visit, however miniscule it might have been, so would it really be impossible to have him included in one way or another in the second?
And who/what/how/when/where is Scar's Ghost? I don't think there really is an explanation for it. The Journal calls it a manifestation of the evil in Scar's heart preying on the weakness in Simba's. Wait, evil can do that? Hmm... What makes Scar so special that he can do that? aside from Lion King being Nomura's favourite movie. He did become a Heatless that kept his original form, who else did that?
Ah, yes Ansem SoD, the most powerfull Heartless in existance but his Darkness/evil couldn't manifest and... Oh wait, Reverse/Rebirth, it is litteraly the manifestation of Ansem's darkness haunting Riku in his self-doubt.
OMG, one of my absolute least favourite worlds in the series, might actually have had a connection with CoM despite KHII pretending it never existed.
Letting your thoughts out sometimes let you get a completely different view on things.
Then there are the worlds where the Organization actually interferes. Why exactly did they not do that before?
There were plenty of Heartless before, so nothing would get in the way of their big master plan. Now, however, the worlds have been overrun by Nobodies, so their plan to collect hearts hurt by the lack of Heartless.
Now you may say, "That's just gameplay", but this series has a habbit of always explaining gameplay stuff in its story.
Eg. GBA Card system is the law of Castle Oblivion, or "Sora has to start at level 1, he must have forgotten everything that happened previously."
The Heartless are missing in the worlds.
Sorry for the wall, I guess I had a lot of things on my mind growing during the ten years since KHII's release.