It's complicated, and I think it's very dependent on the sociocultural climate where those people live.
I've known a few Italian-Americans, second generation, so they were born in the US to Italian parents, or they migrated there when they were little children, they told me their parents didn't want them to speak Italian for fear of discrimination, yet, once they reached adulthood, they wanted to learn Italian and, understandably, they had a hard time and could not master it.
My high school English teacher's family moved to the US when she was 2, she learned Italian when she moved back to Italy to study. One of my English professors in University was born in Canada to an Italian father and a Chilean mother, she can't speak Spanish and she learned Italian when she moved to Italy.
My father has cousins living in France, they were born to Italian parents, but they can't speak Italian at all and never cared to learn it.
I've met people who moved to Germany, Belgium, Switzerland and the Netherlands, all of their children speak Italian fluently, even those born to a non-Italian parent.
So, why? I know that Italians in France didn't face discrimination, in the US, in the past, they faced some discrimination, in Canada they didn't face any discrimination, but they did have rough times in other countries and, I think that's the key motive: when you're feeling discriminated you will tend to withdraw yourself from the group - a society or culture in this case - by which you're feeling discriminated or excluded, and you will look for a group that will make you feel accepted, which will be your own society and culture, you'll hang out only with your compatriots and stick to your culture, and you will try to pass those things on to your children.
But this behavior poses two problems.
First problem is the one reported in the article, it's extremely difficult to master a foreign language when you're older, and I can see that on myself. I'm a linguist and I've started studying English and French when I was 11 years old - I'm 38 now, and still studying - it was easy to learn those languages, I can speak them fluently, retain new words and, if I really put my mind into it, I can conceal my accent but, being a linguist, I've tried to learn new languages in my 20s and 30s (Spanish, German, Norwegian, Romanian, Latin, Japanese) and failed every single time, even though I can quickly grasp how a language works (morphology, phonology, phonetics, syntax) I can reach a basic level in a reasonable time but then it's so hard it's not even worth it.
The second problem is more sociocultural, I work in immigration and see this problem all the time, especially for those people whose parents' culture is vastly different from ours (Maghreb, Pakistanis, Indians, Bangladeshis, Eastern Europeans, Africans, Chinese, Balkans), they feel they don't belong. Some of them don't even feel Italians, others end up having conflicts with their parents because they reject their parents' culture, some feel they don't belong to either culture. Inside their homes their parents are forcing their own culture on them, outside it's a completely different world and, many times, their parents do have a "it's either us or them" attitude, especially when it comes to traditions, culture, behavior, friends and partners, sometimes even food.