Think about some of the best and most popular anime you've ever seen... What do a lot of them have in common, other than a great plot? Well if you're anything like me, you find that those anime have as their setting a metropolitan area at some point.
There's one anime that comes to mind faster than the others, and its Bleach. Bleach starts out from Ichigo's perspective as a young guy in high school who lives in a urban or semi-urban area. He can see ghosts, because that's an attention getter lol. More importantly he can see ghosts in the streets of the city he lives in. By combining, supernatural themes and semi-futuristic urban motifs, Bleach has earned itself an automatic ticket to anime popularity. If only for the fact that it appeals toward two large demographics, namely those who kind of like supernatural themes and people who wouldn't mind living in or near a large metro area. Wait I forgot that it also appeals to the plug and play demographic of slightly uncomplicated good guy versus bad guy storytelling. Either way its a good shonen anime that involves a metro backdrop.
Then there's your hit or miss anime, the ones you either like or you watch and move on.
Akira is one of them. You've got some teenage punks, throw in some motorbikes but wait don't stop there add in an experimental agency that imbues people with high potential with psychic powers, and you have Akira! Akira is one of those anime you need a buddy to watch with, kind of like the buddy system used to keep people safe in the city. It has that Blade Runner meets Kill Bill kind of feeling, that also meets you in dreamland (if you're either lucky or unlucky). Moral there, don't cause too much of a commotion, especially on bikes, and quite especially as a nihilistic punk in the city.
Then there's Durarara, also involving a motorcycle and urban life. In it, there's an urban legend about a headless biker and the main character seems to have some run ins with a suspicious biker that might fit that description. Japan, being largely urban due to its small land space is very likely to have a supernatural urban pop culture with one key result being the popularity of urban legends. People from rural or suburban areas aren't keen on urban legends, well probably because of the disconnect or just because they don't believe in a social setting based legend type thing. But people from urban areas are OK with them and accept them as a way of defining their existential journey. Just like a rural citing of a UFO might cause talk in the town, an urban legend could cause a ripple or even a small stir in the large population of a city. Either way, Durara is that kind of anime. That kind of reminds me of the Persona series, especially Persona 4 which has the same theme but with more... crime?
Japan, being the country containing the city of Tokyo has countless Tokyo based anime and also Tokyo-suburb based anime. Even if the city setting isn't Tokyo by name, most anime have a large Tokyo-like city as a backdrop to the rest of the story. The list of these kinds of anime that just use a city backdrop could be endless: Yu Yu Hakusho, Great Teacher Onizuka, The World God Only Knows, C The Money of Soul and Possibility, Love Hina, Ah My Goddess, Chobits, xxxHolic, Birdy the Mighty, Denpa Onna, and the list could probably go on and on... forever!
This might only explain why anime may be more popular among metropolitan inclined persons, more than those who would rather set up their lives in the suburbs or the countryside... So maybe if you're a bored anime fan with nothing to do little-Japan area of your city is your best bet for a fun day out! :D