This seems to be contradictory, or close to it - you say it is railroading to have a story in advance, but that it is a flaw of 4e to not permit a story in advance.

Not to have a story to tell in advance, but telling the story in advance in railroading.
Rather the DM should have a story in mind, but only presents parts of it that are planned. The story is then told by the players through tier actions...
We are still on settings right?
based in the default 4e world
What is that though? The link provided to the PoL info request thread has that default world just set as I have been saying before that thread was created...there is no default world/setting, you have to create it fromt he ground up.
It's a secret, twilight place cut off from the mortal world by a thin and permeable border, where eladrin live in regions of great natural beauty. What more do you need to build a PC than that?
Now admittedly if you'd never read a fairy story or Tolkein or watched a fantasy movie or listened to Wagner's Ring Cycle than you might need more than the above to help you along. But how many players of D&D fit this description? (None that I've ever met.)
So it has vampires that sparkle in it! See that is more info than I had received elsewhere. The Feywild is excised form the game as vampire do NOT sparkle!
What I need is why int he heck creatures from the Feywild, being cut off from the mortal world, are here IN THE MORTAL WORLD?
So is it cut off or not with its permeable border? Make up your mind. Don't flake out decide what it is and then discus it.
To make an Eladrin character, I want to be inspired by something to play it other than it is a version of Nightcrawler that sparkles. (PS: Nightcrawler doesnt sparkle either!)
Eladrin are high-elves that mated with Nightcrawler and then moved into a pocket dimension....still not really inspired to play one.
What I do need, in advance, is what the OP called "atmosphere and vibe". And the 4e books give me this.
To enough it seems it does NOT provide that, ergo "not as popular as it could have been".
When I prep I have a world history and myth,
These are part of the default setting with previous versions set in medieval era. 4th is missing most of the world, and has no real history. Again see the thread linked about PoL being added to and still the default setting is being designed 2 or more years after the game has been released.
Myth? How do the other races view each other in 4th? What stories of the other races are there to offer?
Legolas and Gimli had a reaction through race to each other. 4th edition races are all sleeping together in one tent.
Heavy alteration of alignment could play a BIG part in this lack of myth and world history because nothing was developed to talk about these races interaction, and some of the newer ones are not present in Tolkien et all to derive from.
Well if you do derive from many, then dragonborn are abominations and bad and should be killed, not adventurer with, likewise the demon teiflings should be hunted down and killed.
Does it work for a game? Yes. Was that the intended response from those races? No.
I don't really know what this means, but if you're saying that there is no backstory in my game
Think I am on the Neverending Story analogy here, so it isnt about backstory, but rather the party is always surrounded by The Nothing, until they decide to go in a direction and things in that direction are then created.
If, after reading the 4e PHB, and learning about the fall of Nerath, the rise of Vecna and the Raven Queen, the migratin of the eladrin from the Feywild to the world, etc, etc, you can't think of any richer premise for a game than "kill some randomly generated monsters and take their stuff" then I'm not sure what you're doing playing FRPGs!
Quite possibly the fact that the Raven Queen, Eladrin, Nerath and return of Vecna are things I am not interested in. Such as some not finding the death of Mystra, Elminster, the rest of the Chosen of Mystra, etc dying off as being not interesting.
Just because it is a fantasy story, and I like fantasy, does not mean I will like the fantasy story presented.
Thank you for letting me know that my game doesn't work, and is just a series of random encounters strung together!
You are welcome. Please also note that you designed your world before play started, you said so yourself somewhere, and your JIT was only altering the story, not the entire setting or creating the setting as you had already done so save for the open bits you left for later to JIT with.
Had you not done any of that pre-game prep work, how would your game differ?
Luckily I don't get angry at my players, and I don't set out to screw them over. I set out my own views on the sorts of features of a game that can lead to GM-player conflict in the recent alignment thread that I started, so won't retread that ground now.
Again we are looking at FOR YOU, things such as the alignment thread. that is good that your method works FOR YOU, but as this thread deals with the popularity of 4E is not determined BY YOU for all others.
BTW, did you try changing alignment to being component parts rather than the 9 straight ones, if so how or does that work for you?
As you yourself say, altering something presupposes a prior state. Given that here there was no prior state, it follows that no alteration took place. Generalise this across large scale features of the gameworld, and you have "just in time" GMing. And I know it can be done, because I do it. And I'm not the only one.
But I don't give you that, nor to Mallus. I say that it must exist in a state when the world is created and JIT cannot create the world/setting. It can only alter it the existing states.
I am saying Schrodinger's Cat was in the box and alive. JIT is trying to decide if it is still in the box and if it is alive of dead. With JIT when you check the state you alter it, but you KNOW it had a state it was in to begin with. JIT doesn't give you that state, putting the cat in the box or not to be able to check later gave you the state JIT is checking and/or altering.
Jewelry was/is worn. Your wizard has feet so might be wearing footwear. These are how they are set. JIT is just checking the state and/or altering it, not creating something that never before had a state.