on the left posted:

They do this because the governments hate them and have tried to expropriate their wealth or genocide them in the past, along with a background level of steady racist laws against Chinese.

They are the educated merchant class and hated by the locals for a lot of reasons, and fortunately as merchants and people who are more educated than the rest of the national population, they are able to meaningfully hold their own (and often the lion's share of national wealth, despite being single digit minority).