The attraction lies in a number of places. Partly I suspect that its the strength of women in these stories that gives them that kick. You can have legitimate arse kickers without bending backwards to take account of differences in culture or historical facts about knights. It feels less incongruous to have a female vampire killer in modern day New York or London than it would at the court of Versailles or Ancient Rome. There's also the influence of Buffy and Charmed here, and the idea that in some respects Urban Fantasy taps into the same root idea as the superhero. I suspect that, like Steampunk, there's such a strong cross genre element at play that almost anything can be fitted into an Urban Fantasy setting.
So many of us are urbanites (and likely our families have been for a few generations) which adds to the sense of importance of the urban setting. We're familiar with cities in a way that we aren't with the countryside any more; that's become a place we visit, not somewhere we live. The genre is so popular because it connects to the world we know, on the other it allows us to take that world and recreate it; putting the wonder back into the urban landscape that becomes staid and stale through its familiarity. It allows us to re imagine our world in a more powerful fashion.
The other reason I suspect Urban Fantasy has become so popular is that it allows us to read about traditional monsters like vampires in a modern setting and without all that Victorian nonsense about virgins and wickedness. It casts them into another light entirely, as antagonists, allies or even love interests if you fancy a bit of free range necrophilia. What's more you can mesh them into the world, using the monsters to spice up urban spaces or add a threat to other, seemingly banal places. That dodgy club becomes a front for a vampire coven who use the patrons as easy prey. The kid who hangs out on the corner is suddenly not a potential thug but someone who sees things beyond the measure of the mundane world.
A lot of authors cast their world with huge arrays of monsters in a style I associate with White Wolf's World of Darkness. There's nothing wrong with this but I admit I find it a little tiresome, because it makes the world feel too full. If I hold up the Anita Blake universe and compare it with the Felix Castor one I do prefer the latter because there's only one source of the supernatural and whilst there might be lots of manifestations of the same thing it feels less crowded and less like the world and his wife has turned supernatural. I, hesitantly, would go further and say that my absolute favourite worlds are ones which are not only strange but where that strangeness is largely undiluted - the worlds of Neil Gaiman's American Gods or Tim Powers' Declare. The world's have a neatness that's pleasing and with the supernatural held at arms length they allow the mortal, mundane things to speak for themselves.
In the UK the growth of Urban Fantasy seems to have inevitably led to the creation of a lot of series set in London. I say inevitably because, realistically, London is at the heart of Britain's culture and is the one of most recognisable places on Earth, let alone the UK. There's a chance to instantly connect with your readers if you mention a landmark or a place, other parts of the country don't have this advantage, they're less well known and perhaps as a result largely unexplored by Urban Fantatists. Would books set in Birmingham or Manchester sell overseas? A friend of mine, Loz, complained about this a few years ago but hasn't taken it upon himself to do anything about it (he's not a writer so fair play to him really).
There have been a few books set outside the capital, Emma Newman's Split Worlds novels take in Bath and are partly set in Manchester as well as London, whilst Lou Morgan's Angel books take place in an unnamed metropolis that could well be Brighton. The bulk of British UF is doggedly London based though. A convention taking place next weekend is having an Urban Fantasy walking tour of Digbeth which sounds amazing and I'm looking forward to it a great deal, if only because its a step towards taking the sub genre north to other parts of the country. It also feels in a weird way like a psycho-geography exercise, stamping new meaning on part of the city, which is brilliant.
Another issue is that Birmingham, certainly, seems to do its damnedest to throw its past away. Parts of history are willingly sacrificed to push the place forward. It sometimes feels like the past is irrelevant in a way that it doesn't in London. I suspect that's partially because of the scramble after the mythical 'Second City' status and partially the desire to keep up economically. It just makes it a little bit harder to build a setting that fits the place, the way that Neverwhere fits London. Perhaps other places are the same, (I don't know - how do you feel about it?) It makes me think that, where my hometown is concerned, a slightly different strategy is needed. If Birmingham is so set upon the future then perhaps there's a plot there after all. Beyond that it feels like any urban magic is hidden among the streets, which is arguably where it should be.
To that end, this weekend I decided to start an occasional thing on the blog - grabbing pictures of Birmingham and trying to put together pieces of flash fiction to inject them with the fantastic. It won't be anything I do regularly (too much to do to do it regularly) and it's at least an excuse to do some urban walking and see more of the city.