Interesting. I'm married to a woman whose grandparents came from Norway on her mother's side, and Germany on her father's side. They're long dead now, but her parents said that Norwegian and German were spoken as the primary language by those immigrants until the day they died. They learned enough English to get along, but always preferred their native language. My wife's parents speak almost not at all in their parents' languages, and my wife can't even say hello in either language.
Similarly, I grew up in a CA town with about a 30% hispanic population, back in the 50s and 60s. I had several very good friends who were hispanic. In the first grade, most of them spoke Spanish. By the end of 5th grade, they didn't even have accents. One was my best friend, and I used to spend a lot of time at his house, as he did at mine. His abuela (grandmother) spoke no English at all. His mother preferred to speak Spanish, but spoke English OK. My friend? By the time he graduated from high school, he spoke American English perfectly. He's now the mayor of that town.
Thus it is in immigrant families. Thus has it always been. It takes a couple of generations to completely remove the original language.
Those who claim otherwise simply have no experience with immigrants.
Nice comments.
You are right. My husbands family spoke Portuguese and Spanish. (denpending on the side) He grew up speaking both at home, and learned English for school. (from watching cartoons) He mostly speaks English at home, but it was important to him that our kids learn Spanish and Portuguese. They can speak all three, but rarely speak anything but English. He told my daughter the other day that if she only speaks English, she will lose her ability to speak the other two. She said "I don't care. My friends speak English!"
What people speak at home is their business, but not learning the host country's language is irresponsible. Police, firefighters and doctors, just to name a few, can do their jobs better when communication is as clear as possible.
My Italian told his family that they were in America and they would speak English only; the Italian work ethic was too strong to do otherwise, particularly during the Depression. Besides, with all the other nationalities around, the immigrants needed a common language to communicate with each other and English filled the bill for both social and non-social purposes.