Short answer:

Immigrants tended to lose some of their ancestral foodways and may have to improvise in a new environment that doesn't have familiar ingredients. The traditional cuisine of the British Isles isn't as prized as some others today-- but having enough to eat was likely delicious enough for people at the time. Consider just which populations were coming, when, with what kinds of culinary skills.

Discussion:

Immigrant populations may over-represent population subgroups less inclined to complex cooking- trappers and soldiers, for example. In many societies women have the culinary intellectual capital - but many frontier communities are overwhelmingly male. They may cook just as well as they did “in the old country” - that is, badly. Consider Australia's convict settlers-- did they arrive in Botany Bay with a culinary capital representative of Britain? Or is more reasonable to conclude that many of these unwilling migrants wouldn't have known much about how to plant, cook or fish in their country of origin? We've got evidence that many of the migrants to Australia in the early 19th century _arrived_ malnourished, which explains why they might prioritize calories over cuisine. "If it fills an empty belly, it tastes great".

New arrivals often eat very badly, and even starve in an environment where they don't know what to eat and what to plant when -- traditional societies had enormous reservoirs of social capital, the knowledge of what we plant when. Consider the precarious food [in]security of the Pilgrims and the story of Thanksgiving as one example, albeit substantially a later fiction. While much of "our Thanksgiving story" is invention, one can note the importance of foods available in North America; even as mythology, "the Thanksgiving meal" is part of a process of acculturating the foodways of an Anglo population to a new land.

There's nothing specific about this phenomenon to Northern Europeans: when the Nez Perce Native Americans were forced from their lands in Eastern Oregon and Washington they went hungry. . . removed from the places where their foodways fit the resources, Native Americans had a hard time finding food in an unfamiliar landscape. It takes time to modify an environment, but its do-able, note the enthusiasm with which Anglo settlers plant apple trees wherever they go. One of the projects of the British empire was the inquiry into viable foods for different environments, note that Captain Bligh on the Bounty was transporting breadfruit -- identifying, collecting, and transporting useful plants was part of the ecological/agronomic infrastructure of empire.

The early European immigrants to Australia -- a place with abundant food resources, if you know what to plant and where to fish-- were starving or near at Botany Bay. The Surgeon White described the circumstances in 1790:

"much cannot now be done, limited in food and reduced as the people are, who have not had one ounce of fresh animal food since first in the country; a country and place so forbidding and so hateful as only to merit execration and curses"

The settlers of the First Fleet had some bad luck with weather, but it's also apparent that the seeds they'd brought with them often failed due to unfamiliarity with soils and climate. Their hunting technologies also were inappropriate-- firearms weren't accurate, and Australia's bounding marsupials were accounted very hard to hit- and their flesh unpleasant to eat. They also record very little success fishing. And so when they improvised a cuisine that they could produce, it was pretty monotonous . . . you figure out "what works here", and repeat it. It was meat, veg and a starch like damper a lot of the time-- not tasty, but better than being hungry.

There is some record of learning from Aboriginal Australian foodways, but It took the arrival of Mediterranean immigrants -- Greeks, Italians, and some from the Levant-- to recognize the scale, variety (and tastiness!) of food resources present in a Mediterranean climate; this wasn't something that the Scots/English/Irish who came earlier knew. As an example- the warm waters around Australia have lots of octopus and squid. Greeks, Italians, Lebanese - they’re all familiar with just how nice a meal this can be; they weren’t familiar with the unpleasant surprise of the blue ringed octopus, but they learned that and now octopus and calamari are on the menu in Melbourne and Sydney.

For Canada, note that contemporary eaters don't particularly prize Scottish culinary traditions in the way they do Scottish distilling traditions; for Anglo Canada the Scots are a big influence, and they were a meat heavy food culture. French foodways are more prized today . . . whether in Canada or the US, you'll notice a substantial change in the contemporary status of food in regions with a French cultural patrimony; eg you go to Louisiana for a very wide variety of complex food preparations, you go to neighboring states for barbeque. There's a long discussion about Catholic vs Protestant foodways, French vs British foodways and the like to be had as well. One author notes that many immigrants to Canada got their model menus from food served on the steamship lines that brought them:

[An immigrant's] cooking maps very well onto the second-cabin steamship cuisine of the North Atlantic, which itself derives from the more general realm of American-British cooking.Her staples like steak, roast beef, lamb, peas, and potatoes all appear on representative steamship menus, as do her other dishes: pea soup, griddle cakes, mixed pickles, cranberry sauce, wine jelly, steamed puddings, hard sauce, ginger pudding, custard, coconut cake, biscuits, preserves. [Wack 2018]

For Scots and Irish who'd known hunger, this was likely more wonderful sounding than it is for us today. Even if in steerage - where they'd not have eaten as well as second cabin-- they'd have aspired to this. That "a lot of meat" doesn't sound delicious to us is likely a function of having enough to eat . . . for folks who were hungry and cold much of the time, it was likely plenty appetizing.

Sources

Risson, Toni. “From Oysters to Olives at the Olympia Café: Greek Migrants and Australian Foodways.” Gastronomica, vol. 14, no. 2, 2014, pp. 5–15.

Patel, Samir S. “Australia's Shackled Pioneers.” Archaeology, vol. 64, no. 4, 2011, pp. 44–50.

Staniforth, Mark. “DEFICIENCY DISORDER: EVIDENCE OF THE OCCURRENCE OF SCURVY ON CONVICT AND EMIGRANT SHIPS TO AUSTRALIA 1837 TO 1839.” The Great Circle, vol. 13, no. 2, 1991, pp. 119–132.

Wack, Mary F. “Recipe-Collecting, Embodied Imagination, and Transatlantic Connections in an Irish Emigrant’s Cooking.” The Canadian Journal of Irish Studies, vol. 41, 2018, pp. 100–123.

Smith, Andrew F. “The First Thanksgiving.” Gastronomica, vol. 3, no. 4, 2003, pp. 79–85.

Crosby, Alfred. "Ecological Imperialism: The Biological Expansion of Europe, 900-1900", (Cambridge University Press:1986)

BOYCE, JAMES. “Return to Eden: Van Diemen's Land and the Early British Settlement of Australia.” Environment and History, vol. 14, no. 2, 2008, pp. 289–307.