Now, you see, this, this question I'm not going to do justice too. But as it passes midnight, here's the thoughts I've given a bit of air too. Others can feel free to toss in their own opinion for this, if they'd like.
I think much of this change comes from the authors themselves. Writing has predominantly been the pursuit of the middle class, and those who are (by and large) over educated and with the spare time to dedicate to it, often in the pursuit of art. Art, I've found, is a very middle class concept, for reasons that I couldn't really elaborate upon. (And it should be pointed out that by no means should the idea of all writers being part of the middle class be taken to be ALL writers. it's a generalisation. I can think of about six authors of the top of my head that challenge this.)
Traditionally, then, the over educated members of the middle class with disposable incomes have drifted with more strength to the city. It offers lots of shiny things and has a stronger, more interesting social life within in, in comparison tot he burbs, which at the start, were viewed as a kind of hybridisation of the country, to a degree. And the burbs are for families, and home loans, and a whole lot of other things that have been viewed as the 'get a life' death that is offered up at the start of Trainspotting.
But it goes back further than that. The country and the city began with different portrayals. When industrialisation started, the city was seen as a dirty, ugly, artificial thing that imposed itself upon the land. Even moreso, it was argued that it broke down community values that had existed int he small communities where everyone knew everyone. There was no anonymity in the rural community, whereas the city promoted this, fractured communal bonds, and so forth. (I should really find that Lefebvre book that talks about this. It's called The Urban Revolution, if anyone is curious.)
The suburbs, then, are a form of the country, but have never attracted much portrayal except in a slow lingering death of growup responsibility.
The rural landscape, however, and even to this day, remains a pure thing. It is seen as the natural face of the world, which has always struck me as a very conservative portrayal... but then, is it not true that a lot of the fantasy authors who populated the world with fantasy novels that have people questing through the rural communities, were also conservative men and women? How much homosexuality, non-vanilla sex, racial diversity, and other non-christian values are found in the books that have laid the foundation for fantasy fiction?
(An immediate example of Fritz Leiber jumps to my mind. For his Mouser and Fafhrd, there was sexual obsessions related to their first dead girlfriends, but it is also of worth to note that Lankhmar, which is the base from which the two operate, is a largely urban environment...)
When it comes to the rise of the city now, in fiction, I think what we're seeing is a rise in new authors who identify the city in a more positive light. One of cultural diversity, and possibly just diversity in general. for them, the city equals itself with a lot of positive notions about lifestyles and choice, and it is thus having an influence on the new kinds of fantasy that are being written.
Or so my head suggests at quarter to one in the morning. Hopefully it'll make sense, even.
The Ben Peek Show.
(Fuck, but I'm tired. Why would I write this now? If it makes no sense, don't worry about it. I'm sure holes can be jammed through it like there's no tomorrow, but I thought the idea was interesting, especially one of a change in fantasy fiction represented by the new weird, which is essentially a shift from rural based communities to the city and its fractured boundaries. Or, you know, not.