Big misconception...
It is harder to learn English when you live in a barrio surrounded mostly with Spanish speakers and your close circle of friends all speak Spanish as well.
I would not be surprised if Hispanics who live in either predominantly White neighborhoods or mixed neighborhoods, master the English language a lot faster than Hispanics who segregate themselves in the barrios.
These people do not "segregate themselves" in the barrios of the US. They are culturally segregated into those areas and can't move up and out until after they become familiar with the majority culture.
How can someone live in a place where they can't afford the rent because they can't get decent employment because they can't speak English therefore they must buy their food and their clothing and the other necessities of life where they're understood and can understand what's being said to them. The business owners in these Spanish speaking enclaves speak English and are usually seen lending money or extending credit at illegal or questionable rates of interest and taking advantage of the non English speakers at every turn, reducing their lives to a treadmill of overwork, underpay and no time to learn English. These are people who are barely literate for the most part and are barley functional in their native language or otherwise "Rossetta Stone Proof".
A Dominican contractor installed marble tile in my house a few years ago. The job took them 2 days (I already had the tile and it was a labor only gig). There was one guy (the owner) who spoke English and 3 others working for him who spoke no English at all. I was building a porch at the kitchen entrance at the time and when the others went to lunch, one of the guys stayed and helped me finish the porch. I gave him a propina for his assistance, out of sight of the others. On day 2 the others showed up without him and I assumed a shakedown had occurred. I was probably correct.
My point is that the people who are most vulnerable are usually in the worst position to "pull themselves up by their own bootstraps". Blaming them for their own misfortune is equivalent to scapegoating.
While I lived there a Salvadoran immigrant bought the house next door. The guy worked in a dealership auto body shop for years and when he got off work, he went right to work in his backyard shop. This guy did nothing but work/ He spoke very little English and his wife spoke none at all. He had a grown Son and Daughter who were native US and handled all business transactions for the family.
Sometimes it takes a generation. Growing up in NYC I had friends whose grandparents had emigrated from Italy, Greece, Eastern Europe, Germany and you name it in the Caribbean and Latin America. Most of those grandparents never learned functional English. Why should it be any different for Dominicans?