The other poster had accurate information, regarding there not being a clear reasoning within the community as to why they still dress that way. There are some groups that feel there is spiritual significance to the colors (black being the color of severity, and white being kindness/holiness), and even ensure there are a certain number of white garments worn, so as to out number the black. This is why you will see some wearing white socks. The hats originated in their countries of origin, namely Poland and Hungary, and each group (except for the Breslov sect) can be identified by minute differences in their hats - e.g. Which side the ribbon is tied on, how tall the ribbon is, how tall the crown is, etc. The same sometimes applies to the different jackets and pants worn by certain groups. A person in the know could identify which Hasidic group a person follows just by looking at their clothing. This is one reason they adhere so strongly to their dress code.

Again, the origins are unclear. Everyone seems to have a different story.

Source - former Hasidic Jew

The ringlets are worn to show that the men don't shave their temples, in keeping with Jewish law. They're called peyot. Non-Chassidic Jews wear them too, just shorter. The tall hats have varying origins, depending on which one you mean. The fur hats are called "streimelech" (streimels) and their origin is somewhat obscure. Most Jews who pinpoint an origin refer to antisemitic laws in a town in Eastern Europe which prohibited Jews from wearing any fur but the tail. Since fur was considered a mark of the aristocracy and the tail was considered the least valuable and most common part of the hide, this was meant to shame Jews. As an act of defiance, the Jews sewed the tails into hats that they only wore on Sabbath, as a special and expensive garment. However, there are many versions of this story, and it exists solely as an oral tradition, so there's no reliable documentation for it.

FWIW, you're seeing the most visible Hasidic Jewish population of New York.

There are a lot more Jewish New Yorkers around, who aren't Hasidic and don't wear such distinctive clothing. Some wear a kippah every day, others don't. You probably won't notice most of them on the street.

Why you don't see as many Hasidic people in California - probably because of differences in New York and California's immigration history. The largest wave of Jewish immigration to New York came from 1881-1945, mostly coming from eastern Europe. The assassination of Alexander II of Russia was popularly blamed on "the Jews," leading to mass increase in pogroms and anti-Jewish laws, then of course the rise of the Nazi's. Over two million Jewish immigrants/refugees came to the US during that time, about half of them to New York.

California's Jewish population started being established during the mid-1800's Gold Rush. They came from all over Europe and from the US, and were attracted to California by economic prospects, rather than coming to New York as refugees.