George Will nicely phrased it - the immigrants were "pyschologically guillotined". After they arrived they could get by with native language newspapers and enclaves but by the third and fourth, if not the second generation, their families had integrated and become Americans. I knew many an immigrant family, even as late as the '40s (yeah, I'm THAT old) where gramps spoke only the old country language, his kids were bi-lingual, and their kids spoke only English. As per the poll, these newbies don't want to become Americans, just live like them.
There was also an deep appreciation of the opportunites here compared with the Old Country. I worked with a Russian Jew who, one day, showed me his property tax bill. I thought he was bitching about the amount (this was California) and I agreed that it was high. he said, "What are you talking about? In my country I couldn't even OWN property. Now I am a Land Owner!"
Well here in CA about 5% of Mexican boys even graduate high school. Lord knows how many tens of thousands a year their families cost the state in support, food, baby sitting services, housing, medical and education.
If we had something besides a dysfunctional immigration system we could figure out how to get that 20% instead of the 69% Mexico is sending, btw...the ones Mexico WANTs out of their country....
[snip]* An overwhelming majority (69 percent) of people in Mexico thought that the primary loyalty of Mexican-Americans (Mexico- and U.S.-born) should be to Mexico. Just 20 percent said it should be to the United States.