Because, as explained below, assimilated Americans have been wimps when it comes to spicy food. We’re getting better.

And Italian food has helped us along the way.

In terms of the “super grande” sized nationalities who immigrated to the United States through 1920, Italians were among the latest to arrive. That meant two very important things for the future of “Italian” (Southern Italian-American) food. First, there wasn’t as much room on farms and city life was more economically appealing anyway. Second, it was smack in the middle of two trends in WASP American attitude towards food. On one hand, the attempted scienceification of everything (“racial science” much? calculating what species of fish ha probably swallowed Jonah?) absolutely extended to food. Nutrition scientists of the time believed the blander the food, the healthier. This was inextricably bound with the fact that currently arriving immigrant groups, especially from Italy, China, and the Near East, all enjoyed significantly spicier food than America’s dominant palate. In the case of Italy, garlic in particular.

For those of you thinking, "But Italian food didn't/doesn't have that much garlic!": consider that, if American moralists had a problem with that much (little) garlic, just how bland and how very little garlic we're talking about for waspstream cooking.

But if 1900 America was going to reject Neapolitan and Sicilian cuisine, immigrants from Naples and Sicily and the rest of Italy were going to reject the heck out of American food. Italian-American girls taking summer or school-year classes at Bostpn’s North Bennet Street School, for example, might have to sit through cooking in addition to sewing. But, as the school’s official mournfully noted, some “foolish mothers” insisted on teaching their daughters at home because they thought they knew better. And Italian-American women set up the tools to pass on their foodways. The urban garden isn’t a hipster rooftop phenomenon today—Italian-Americans smack in the middle of cities were planting corn, raising rabbits, and of course harvesting the all-important garlic in private gardens made of whatever green space scraps they could find and buy. And in the face of muscular masculinity advocates pushing meat, meat, meat, the immigrants from lower class backgrounds insisted on preserving the dominance of cheese and oil in their food. Also, insisted on men doing some of the cooking, especially for working lunches. Additionally, the Italian Catholic tradition of a few enormous, multi-generational extended family/community meals every year meant a large concentration of women cooking together, what they knew, passing it on.

But of course, amidst all of this, Italian-Americans were also going to external work, not just domestic labor. And in the late 1800s-early 1900s, one of the things that meant was buying lunch at a “food wagon” (food trucks: also not new!). Given the propensity of immigrants from the same country to settle in the same neighborhoods and even join the same work crews, that lent itself to targeted food wagons run by other people who knew how to cook the same food. And Italian-Americans in particular, with their contentious relationship with waspstream American food, set up standing restaurants, too, in large numbers—especially in the northeast and in cities further west (Chicago usually being the exemplar here).

So Italian-Americans are eating adapted Italian, mostly souther Italian, food. How do we get to Brenda and Eddie and a bottle of red?

First, the French. Immigrants from Northern Italy, in the later 19th century, had gotten into the more upscale restaurant business, which at the time meant French cuisine. But they brought their bordering-France Italian spin on things in teeny tiny amounts—spaghetti not cooked to oblivion, the mandatory glass of red wine.

Italian food was ubiquitous, Italian restaurants were ubiquitous, Italian food was cheap. There were two major stumbling blocks that new restauranteurs had to hurdle: lack of meat and landslide of garlic. As to the first, well, that integration in the Northern Italian-American restaurants went both ways, and it wasn’t limited to restaurants. The conversion of popular dishes to carnivorous versions played out in reverse of medieval cookbooks offering nut-and-cheese alternatives for Lent. Eggplant parmesan (really) got whatever kind of meat was on offer. The workaday pasta course got mixed with the special-event meat course to make spaghetti with meat sauce variations. “A taste for meat...is acquired in this country,” a satisfied domestic scientist remarked in 1922. Immigrant Antonio Ranciglio of St. Louis (renowned for its fine Italian cuisine). exulted, “Here I eat meat three times a day, not three times a year!”

As to garlic, the outward appearance is that dish by dish, Americans got more used to eating food with...some...garlic. An interesting point to observe, according to Nacy Verde Barr and Mark Zanger, is that the 1920s and 1930s, when Americans of many backgrounds are turning to the comforting, cookie-cutter-on-purpose checkered tablecloth world of midcentury Italian restaurants, is that this is when garlic bread starts appearing on the menus. Zanger hypothesizes that restaurant chefs’ replacement of the bread-and-butter routine with garlic bread (or with white bread and olive oil) helped get waspstream America on board with amounts of garlic vaguely more palatable to the people cooking the dishes in the first place—still, of course, a major market share. I’m not sure how much we should attribute any kind of specific motivation here—garlic bread is not exactly groundbreaking cooking show-level invention—but it’s at least a good illustration of the growing acceptance of garlic and Americanized Italian food in general.

Then in the 1950s and 1960s, Domino’s and Pizza Hit will invent pizza delivery, to the extent that by 1970 it becomes a weapon in the government spying on suspected dissidents.

I think by then we can say, Italian food had become American food.

I’ve explained the factors specific to the rise of Italian-American cuisine. I hope that helps show that there isn’t a “default” of successful preservation of foodways that we should look for from every immigrant group. It takes a lot of factors building off each other.

Hasia Diner’s Hungering for America is a great and fun source if you want more information on the history of Italiam-American food in America. ...And it might help with the reat of the question, because the book’s subtitle is Italian, Irish, and Jewish Foodways in Age of Migration.

But I have to go to Spanish class now, where, sadly, we will not be cooking.

I have no knowledge about this topic, but the people who provided answers to this related question clearly do, and provide lots of information about Dutch (/u/lord_mayor_of_reddit), Irish (/u/Cenodoxus) and Native American (u/sunagainstgold) cuisine.

I hope this is allowed by this sub's rules!

EDIT: a friendly bot reminded me to add user pings to the authors of the answers.

I think I'd debate the idea that Eastern European cuisines aren't popular in the US, particularly in the Northeast or Midwest.

Of course "from the pre-1917 Russian Empire" is not the same thing as "ethnic Russian". A huge proportion if not the majority of Ashkenazi Jewish immigrants to the US in the late 19th and early 20th century came from the Russian Empire, and kosher delis, bagels and lox are definitely a presence in the American food landscape. I've never seen a breakdown by nationality, assuming that one would even make sense pre-Soviet nationalities policy, but remember that when immigrants came to the US from "Russia", they were if anything more likely to be Ashkenazi Jews, Poles, Balts, or Ukrainians than ethnic "Great Russians".

Even within Russia, what counts as "Russian" food can be a hotly debated topic among gourmands. Many of the most popular dishes across the former USSR come from the USSR's Book of Tasty and Healthy Food, first published in 1939, that attempted to create a pan-Soviet cuisine. As a result, plenty of Russians eat Ukrainian borscht, and Georgian/Caucasian shashlyk, and wouldn't necessarily consider themselves to be eating "ethnic food". Interestingly, the book was spearheaded by Anastas Mikoyan, then-Peoples Commissar of the Food Industry, who also imported and adapted certain food processing techniques from abroad, such as adapting Chicago-style bologna into "Doctor's Sausage", which retains a big place in Russian food (nb: it's better than bologna).

Perhaps one unintended result of this is that nowadays you have chefs like Maksim Syrnikov who champion an "authentic" Russian cuisine (no Ukrainian borscht! No potatoes, since they're from America!), but even in Russia it's not really how people eat.