Folks,

You're welcome to comment with examples of other ethnic enclaves in the US, thus answering the initial assumption of the OP. If you do so, however, please make your discussion of them thorough and substantive. Simply linking to a site about an ethnic community, or simply mentioning the existence of one, is not an acceptable answer.

Thanks!

San Francisco is the area I know best, so I'll try to summarize by ethnicity:

Chinatown dates back to the Gold Rush, when a largely Cantonese-speaking population came into the area to work the mines. This group faced a large number of challenges in the form of race riots, the Chinese Exclusion Act, residence restrictions, and even a quarantine due to Bubonic Plague, all of which had the effect of concentrating people in Chinatown. It wasn't until the mid-1900's that people were able to move out into other parts of the Bay Area, so now many Chinese Americans who visit Chinatown live elsewhere. A newer wave of Mandarin speakers has also appeared in the last few decades who settle in other neighborhoods.

Japantown was largely depopulated due to internment, and after the war it was eventually rebuilt as a shopping area without a large Japanese-American population. Many of the homes in the area were eventually destroyed by urban renewal in the 1950's and 60's.

San Francisco has never had a large Korean American population, but there are some Korean businesses and restaurants around Japantown (possibly this presence dates to the Japanese occupation), and a consulate. I believe much Korean immigration dates from after the Korean War, when segregation was a little less strict, so many settled in other parts of the Bay Area such as Santa Clara, which has areas similar to LA's Koreatown.

SF did host some members of the Korean National Association in the early 1900's, but their interest was in returning to Korea.

Your assumption is flawed to begin with. Western cities are littered with Koreatowns, Little Tokyo's, Little Italy's, Russian emigre enclaves, Little India's, etc. There are various Greek communities in major cities all across America that network with one another, the most obvious one probably being Astoria, NY. There are huge neighborhoods all over the Northeastern United States that are majority Italian-American and covered with Italian flags, and several Little Italy's (official or unofficial) in the 5 boroughs of New York City alone - one in the Bronx, one in Manhattan, and then several unofficial ones all over Brooklyn and Staten Island. There are Orthodox/Hasidic Jewish communities - of Central and Eastern-European descent - in almost every major tolerant country, and they've maintained large insular communities that are so successfully isolated from the cultures around them that three Hasidic Jews raised in New York, London, and Australia will have accents more similar to one another than they do to people who live three miles away.

This may go against the rules of the sub, but it's worth noting that this is a question that has an assumption that could've been solved with a simple googling of "Koreatown", or "Germantown", both of which are mentioned in your question (though it's worth noting that Philadelphia's Germantown is now more Italian than German). In Los Angeles alone you have a Chinatown, a Koreatown, a Little Tokyo, a Little Armenia, Little Bangladesh, Little Ethiopia, Tehrangeles (Iranian emigres), Thai Town, and Filipinotown. If you google "Little Russia" your third result is Brighton Beach, NY, where for several blocks most of the signs are in Russian. And that's not even the only Russian enclave in New York City, since there's another one in the Bronx! Even for less recent immigrant groups there is some preserved insularity.

All my answers are focused on North America, but you could just as easily seek examples from Europe or China. London, for example, is a hodgepodge of ethnic enclaves.

If you're from North America or Western Europe, Chinatowns may appear more prevalent because of a few factors - the distinctive architecture that's common to most of those Chinatowns, the bus networks that link the Northeastern US's Chinatowns, and the fact that a lot of Chinatowns tend to announce themselves through an official-looking entryway like this and go further out of their way to court tourists than your average Indian or Italian neighborhood might go.

From your posting history, it looks like you are from China and now living in Taiwan. If you are Chinese, it would make sense for you to know a lot more about Chinatowns than you know about any of the many Little Italy's.

Anyway, I realize that this answer doesn't totally fit the normal standards of the sub, but the question is so far wrong in its assumption that I feel that answering it simply doesn't require an extensive historical explanation, any more than the question "Why aren't there any blues bars in Chicago?" requires an explanation other than a big-ass list of blues bars.

For a reference to other "immigrant"-towns, there are a few that I am acutely aware of.

Mexicantown in Detroit, which started forming in the 1940's but was only branded as "Mexicantown" in 1980's. It grew significantly during the 70's and 80's, and is a well known landmark in Detroit.

Also in Michigan is the town of Frankenmuth. Not exactly named "Germantown", it is sometimes referred to as "Michigan's Little Bavaria". It was settled by German immigrants in 1845 and the entire town is steeped in German influence, as most buildings have a Franconian style. It's a huge tourist attraction, especially during Christmas because of Bronner's Christmas Wonderland.

Koreatown in Los Angeles, which received some national attention during the L.A. Riots in 1992 when some Korean store owners camped on the roofs of their stores with rifles to protect their businesses. L.A.'s Koreatown, like another Koreatown in Toronto, started forming in the late 1960's due to more liberal immigration laws, and the desire to leave a war-torn Korean Peninsula.

There are other "immigrant"-towns in various countries. Certainly there are some Chinatowns that are more well know, but even a simple Google search would have shown that other versions do exist.

I have done a fair amount of research about German immigrants in the U.S. and the simple answer there is: German immigrants held on to their language and maintained their communities quite carefully up through the 19th century, but when the First World War broke out, there was anger and violence directed at German-Americans, so they did their best to blend in better. And by that point, since Germans were considered, ethnically, white, they were able to do so more easily than, say, the Japanese-Americans, who were targeted during the Second World War.

I don't have my books with me right now, but I know, for example, that there was a Little Germany in Manhattan that fell apart around the turn of the century, and there were a large number of German-American newspapers that went out of business around the time of the First World War. The number of German-only and mandated German-English bilingual schools also dropped significantly around the First World War.

Additionally, according to the 2010 U.S. census, people with German ancestry are still the largest group in the U.S. (outnumbering people with British ancestry by far), and if you know what to look for, it is easy to see that a lot of German culture has seeped into American culture, which means that the old German neighborhoods and institutions do not stand out as "foreign" in the U.S. in the same way that a Chinese grocery store still does.

Because most of us can agree that this question rests on an incorrect assumption, I think the better question might be why it APPEARS as if there are more Chinatowns, and why they seem so much more obvious and distinct than other neighborhoods.

To that end, I'd start with literature and popular depictions, where the orientalism and exoticism of Chinatown carried more dramatic possibilities to an English-speaking, white audience than more European alternatives. The trope of the Chinese toy shop, medicine shop, or other shop sets a lot of plots in motion, particularly when mystical themes are involved. In more modern works, Chinatowns have remained popular (if less common), often serving as setting for plots involving organ trading in addition to the older magical talisman topics.

Meanwhile, the North American Chinatowns can be said to have been "branded" very well. The architecture, types of stores, and goods available remain largely consistent from Chinatown to Chinatown. There's even a familiar entrance to Chinatowns, an arc that appears in Los Angeles, London, Boston, Philadelphia, and others. They also tend to be very tourism-friendly, with an abundance of restaurants and shops with toys, gadgets, baubles, and artwork. Other ethnic neighborhoods, such as Hasidic, Caribbean, or Greek ones, tend not to be as tourism-friendly. You can go down Steinway Street in Queens right now and see several blocks of middle-eastern shops, but most of them just sell groceries and hookah.

Most of these Chinatowns are also around a century old (or older). They've had longer to build their brand (so to speak) and there has been a steady stream of immigrants to keep the neighborhood demographics more constant than their German or Italian counterparts.

If somebody else can provide more details along these lines, I think we will be closer to an answer that is more useful to the OP than "you're wrong" (though OP is still wrong).

There's a Koreatown in LA