From the perspective of someone who is not living in a large city I think you are primarily talking about the properties of large cities, not about assimilation in general. Large cities tend to form an excessive amount of enclaves because they allow hyper specialization. I always hear about people wanting to live in large cities because you can find a large group of people or go to businesses specializing in what you like no matter how niche your interest is. Cultures are not exactly niche. Millions of people can share the same culture.
However, what you seem to fail to grasp is that what you are seeing isn't actually the native culture of these people. It's actually an "americanized" (or localized) version of Bangladesh culture. If you forced them to go back to Bangladesh they would be considered too "americanized" and treated almost like outsiders there.
However, what you seem to fail to grasp is that what you are seeing isn't actually the native culture of these people. It's actually an "americanized" (or localized) version of Bangladesh culture. If you forced them to go back to Bangladesh they would be considered too "americanized" and treated almost like outsiders there.