Eric makes solid points here; I'm going to emphasize one of them.
I suddenly had a flash of interest in seeing what you, John, would do in Pearl Harbor. The cause of that flash has long been forgotten, but the sense of it remains: if you were in that world, would you alter it? O.K., so why did I give you to Adam? The answer is simple: I have no idea what happened at Pearl Harbor. Some Japanese planes attacked, coming in from an unexpected angle, and the Pacific Fleet was hit hard, but I don't know what angle or how hard. I don't know enough to know who would have been in charge of anything there. I saw the movie Pearl Harbor, but was told by a marine steeped in military history that it was not merely factually inaccurate, it was directly contrary on many important points to the actual events. I would not have felt comfortable attempting to run my own sons in that scenario, because I did not know the scenario and I did not have time to learn it. I looked for someone who did.
Had I decided that the Titanic was the place for you, probably John Walker would have been asked to run you (and maybe you'd have killed each other by now), because he's been working up a Titanic scenario for some time and knows the facts quite well. I could run it, but he would be much better. Certainly, though, I could not have run him in that scenario; he'd be all over me.
I have run E. R. Jones in Narnia. He's never read Narnia, and I've read it several times. I would never dare to run him in Xanth, as I've never read it and he has, so most of what I know of it comes from him.
We tend to stick with what we know. I run the same worlds with new players quite frequently, and it is not merely to test those worlds; it's because they don't require as much work on my part, as I've done the prep already and I've had the bugs knocked out by people who played them hard.
Besides, if you ask me to run a world, and I comply, odds are better than even that I'm going to disappoint: my conception of that world will not match your expectations. That's why Eric says that it's fine to ask whether you want hamburgers or pizza, but not whether you want McDonald's or Ruby Tuesday, Dominoes or Pizza Hut. If you ask me for fantasy, you'll probably wind up with Dancing Princess, NagaWorld, Bah Ke'gehn, or Dungeons & Dragons, and if you're thinking of Labyrinth or The Dark Crystal or Narnia you're going to be disappointed. Ask me for space travel and my top choices are Mary Piper Beta, Starship Destiny, and Blake's 7, not one of which is Star Trek or Star Wars or Battlestar Galactica or Babylon 5 or Red Dwarf.
In fact, these kinds of questions, to my mind, don't really convey what you actually want in a game. For example, if what you want is combat encounters, then it doesn't make much difference whether you're in a swords & sorcery, a post-apocalyptic, a film noir, a superhero, or a space opera--any one of them could provide the action you want, and any one of them could fail miserably. Yet working out what it is you really want is not so simple as asking what books or movies you like. Did you like Lord of the Rings because of the great battle sequences or because of the strong moral conflict or because of the wonderful landscapes and peoples? Was the appeal of Die Hard in the heroism, the incredible odds, the humorous quips, or the demonstration that he and his wife really loved each other despite their problems? You probably can't tell me what would make a good game world for you, because frankly you probably have less of an idea than I do. I'm watching you, and seeing what makes you smile, makes you respond, gets you excited. I pick worlds to get that reaction again, to see whether the same thing in a different context works, or whether something different also works.
It might be said that the players are playing the game, but the referee is using the game to play the players. I know at least one person who will not play Multiverser with E. R. Jones because they know how well he uses it to get inside people's heads and "psyche" them. It's part of what a referee does in these games: figure out what makes his players happy, and how to give it to them in a way that will be interesting and exciting along the way.
Don't worry. Everything you say about what it is you like is taken into account. The one thing that will not happen, though, is no one will send you where you say you want to go next, because that would be the most boring and predictable outcome possible, and the game is not allowed to be boring or predictable.
--M. J. Young