This is what happens to communities that have a wave of immigration, especially when it comes to refugee populations.
They are a snapshot of their culture in that period and it mostly stays stuck in time, especially with regards to language.
Meanwhile, a couple of decades on, the country’s language has continued to develop and change as all languages do but the migrant language remains basically as it was.
French Canadians are a good example of this, since the split was 300 years ago
Isn’t there a thing that Bostonians sound more like old English than the English?
Yeah i read that too, where the accent we yanks associate with British today grew from an upper-class affectation that developed after the war?
No, they have simply developed in a different direction that is in some ways more conservative and in some ways more innovative. It’s not a really a good comparison to a single generation of an immigrant family.