How many of those folks speak Spanish as their first language? Just the older people, I'd guess.
The major growth in Hispanic population areas comes from new immigrants, not births. Those that arrive any older than about 15 or 16 will almost exclusively work, think... and listen to music in Spanish. In the Southwest, something like 65% of Hispanics are now first generation. If you add the flood of new immigrants from the last two years, that figure will go up enormously. And the more "Spanish only" speakers, the stronger the Spanish speaking community gets.
Add to that the fact that in many highly Hispanic areas, many jobs are "Bilingual preferred" and, after EEO is factored out, people who speak English only don't get jobs at stores, service organizations, hotels, even hospitals and law enforcement.
Most of the young folks of Latin American ancestry that were born in the US since the 1990s (or maybe earlier) speak English better than I do. I would have to think that they're listening to the same music, either via radio or online, that their non-Hispanic friends do.
Those born here are second generation, and almost as an inviolable rule, they are bilingual. But they speak "kitchen Spanish" with no correct grammar, usage and spelling.
In markets with huge percentages of Hispanics, most live in a community where the original immigrants never have to learn anything but basic English, and they retain their culture, their language, their music tastes and diet from the homeland.
That's no different than the kids and grand-kids of other immigrants in the last 150 years. My dad's family came over on the boat from Germany in 1900. My great-grandparents had to learn English, and spoke it with a German accent.
Today, with huge Hispanic communities in many, many markets along with services that will speak Spanish or get an interpreter, there is far less learning of English by original immigrants than ever before.
When one of my daughter was at a mainland US school 40 years ago, she was punished for speaking Spanish at recess. Today, she would be celebrated for being bilingual!
Their kids, my grandfather, aunts and uncles, were bilingual. My dad and the other relatives of his generation spoke no German whatsoever.
Today, by third generation, Hispanics generally know only enough Spanish to order at Taco Bell.