So, I'd actually push back on that and say you will find cities with a variety of "new" immigrants and related community cultures stacked on top of the older immigrant communities that are still there (think your various Eastern Europeans). It makes for a unique mix.

There's a variety of reasons for this I could speculate on, and three of the firmer ones are refugee resettlement (Minneapolis and Somalis, pre-cool Cali and Hmong, Michigan and Syrian refugees), Central/South American immigration patterns beyond the border states, and military bases which tend to show up all over the midwest/west/southeast/southwest (Korean, Vietnamese, German and maybe smaller ones but those stand out).

These communities exist alongside the traditional cultural elements of the city and can often be blocks away. But, the areas tend to look a lot less like Chinatown and more like Flushing - maybe more insular, but still plenty authentic.