IMMIGRANTS BRING A “FRAGMENT” OF THEIR SOCIETY WITH THEM. The idea that you speak a dialect frozen at the time that your relatives emigrated reminds me of a book by Lewis Hartz that I have always found persuasive. The book is THE FOUNDING OF NEW SOCIETIES. This wikipedia entry summarizes the argument that Hartz developed: “the idea that the nations that developed from settler colonies were European “fragments” that in a sense froze the class structure and underlying ideology prevalent in the mother country at the time of their foundation, not experiencing the further evolution experienced in Europe. He considered Latin America and French Canada to be fragments of feudal Europe, the United States, English Canada, and Dutch South Africa to be liberal fragments, and Australia and English South Africa to be “radical” fragments (incorporating the non-Socialist working class radicalism of early 19th century Britain)”
Just as immigrants did not experience the evolution in their mother country’s culture, so their version of the mother country’s language was not affected by the evolution of that language.