> During World War I, German-Americans had good reason to lose
> their national identity.
By which, I presume, you mean hostility of the "native" population. But by the same logic, Hispanics, Russians or Poles should follow the Pennsylvania Dutch footsteps, but they often do not. Clearly, something else than potential hostility must be going on here.
My explanation, informed by the views of Thomas and Znaniecki on immigration (_The Polish peasant in Europe and America_) and Max Weber (The Protestant Ethic and the Spirit of Capitalism_) on modernity, is that immigrants who come from "collectivistic societies," such as Eastern Europe and Latin America, have a harder time adopting to "individualistic societies" such as the US - and their coping strategy often relies on cultivating collectivism and nationalist identity politics. The Germans, otoh, who for the most part are not a collectivistic society - have it much easier to adopt to the US culture and lose their old-world identity, instead of cultivating the old-world nationalistic identity.
Wojtek