There are two factors here... at least!
First, second generation and later Hispanics don't get formal Spanish in school. So they tend to speak... if they do at all... Spanish with family and friends but not at work, particularly if they have an "anglo" employer.
Second, assimilation by those born here means they pick up on the music and lifestyle of the USA, not of Mexico or Honduras or Cuba. Kids like to be part of a group that makes them feel good, and that usually means speaking English and "being American".
In some places like San Antonio and Albuquerque and Fresno we have things like the Tejano culture in parts of Texas... a blend of some things Mexican and some American but very distinct.
But there are still inner cities in large markets where an immigrant and their family can get by very nicely only speaking Spanish with just enough English to get through school. Those communities tend to be the ones we jokingly say "you need a passport to go into" because they are so culturally different from the typical middle class neighborhood of the same metro areas.
A few take advantage of it. One of my daughters is a lawyer and does visa work for multi-national companies that need visas and work papers for employees and contribuitors to come to the US or to go and manage a division in another country. She has law degrees in four countries and can write lawyer-talk in 6 languages: that gives here a big advantage over the lawyer from someplace in the Midwest who only does English and thinks the "problem with France is that there are too many people who don't speak English".