There's almost 0 state efforts to preserve the cultural identities of immigrants of any kind
When people celebrate "diversity" in the West, it's just eating shawarma, drinking boba, watching Anime, listening to kpop, and eating at an Ethiopian restaurant. Pure commodification and consumerism masquerading as celebration and promotion of foreign cultures
Or you'll have people fetishizing about spicy latinas, lightskins, and Asians like they're fucking Pokemon cards
when i was a kid, the view i got about the US from media about immigrant experience was that assimilation was the most important thing, learning english, changing you name to an american one, acting like an american, etc. i imagine most immigrants going to the US also have similar views and for example dont teach their kids their native language thinking it may make it harder for them to assimilate, and US society also dont make that easy since many places like public and private ones only speak in english or even are hostile to people speaking in any other language than english.
those factors plus not living in an area with people from your birth country background eventually leds to many 3rd gen migrants that dont know their granparents original language