There is nothing the least bit complex about this. Prior to the establishment of the Welfare Nation,immigrants came to America because they would be free here to work hard,profit from their work,and make better lives for themselves and their children.
They wanted to be Americans,and they wanted their children to be Americans.
Now the vast majority of them come here to retire in place with "Free" housing,clothing,food,utilities,medical care,education,and a nice check each month to spend on anything they want to spend it on.
They could have remained at home in whatever Shitstainistan they came from ,and not lived so well as the day they set foot in America if they had been able to live and work for 200 years at home.
The ones that come today have no desire to EVER become Americans. In FACT,they want America to turn into the countries they came here from,except they still want to keep all the free stuff.