I think the only way an ethnic ghetto can last is if it gets a regular pilgrimage from “the old country”, to reinforce the old ways and introduce the new generation to them.
George Will 's articles occasionally give me heartburn, but he coined a classic phrase when talking about our early immigration. He said those Europeans were "psychologically guillotined" when they came here, and had no option other than to assimilate in order to be successful.
LONG ago, when I was in my teens, I asked my dad, who came over from Germany in the '20s, to teach me German. I got "whopped upside my haid" and was told, "You're in America, you don't need it." I told that to an Italian friend of mine in school and he said that his dad said the same to him.
Fast forward 60 years and I am a volunteer reading tutor in a Nevada Middle School, bringing kids a couple of grades behind up to speed. I correctly surmised that most would be Hispanic, due to their influx, but was wrong on why they were lagging. It seems that their fathers wouldn't let them speak OR READ English at home. "Spanish is your heritage." they were told (info via the teachers).
There's the difference. These people are not guillotined, as you say, they get constant reinforcement from the Motherland. They don't assimilate, they colonize.