Personally, I suspect that alot of the Argentine problem is due to oversupply of meat. I ate in the homes of Moroccans who would be lucky to get meat once a month. So when they got it, they would get odd cuts and would have to get as much value out of it as possible; so you get these mouth watering braises and soups that seem to go on forever. Otherwise they make great use of what they can get their hands on: beans, lentils, vegetables, fish...
Here on the other hand, there's never been any need for invention, and vegetables and seafood get scorned. If the problem is lack of diversity here, it's a self-made prison.
I think you've nailed a big part of it right on the head. Immigrant communities, especially over an extended course of time, are highly influenced by the availability of ingredients and local cuisine in the country they come to, and it shapes the cultural exchange that takes place.
I think of Italian food as a good example. So many of the wonderful dishes and ingredients you get in Italy weren't the by-product of a conscious effort at producing delicious cuisine. They were born out of the reality of a largely peasant population in a Meditteranean climate with limited access to food options. Meat was expensive and in limited supply, hence the use of pork/chicken/seafood rather than beef, as these were better suited to the region than grazing beef cattle. Ditto for the fact of unique cuts, all types of sea creatures and even offal - couldn't waste it. The variety of great cheeses was because every community had to do it for themselves, using the milk (and whatever that creature ate) and preservation practices that worked best there. The herbs and vegetables were what they could get and grow in often limited spaces. The olives and wine had ancient provenance and were long staples. Grains were unrefined because the means were simple.
What we've then seen over the past couple centuries is first the wealthy and ultimately the broader population take the simpler inspirations and refine them as scarcity became less of an issue.
But put yourself in the shoes of an immigrant family from Italy in say 1910. Italy was generally quite poor at that time, and you're an economic migrant seeking a new life in Argentina. Suddenly, luxuries you couldn't dream of are cheap and in plentiful supply. Beef cuts for a fraction of the price in Italy. Milk and mild cheeses, as opposed to strong and rock-hard types you might have had in Europe. White breads. And furthermore, you don't need to make them yourself, but just go to a shop and buy them. So you trade your old ingredients (now hard to find) for what you may assess as more desirable (and obtainable) ingredients in Argentina. The tradition starts to break down...
And as Joe indicated, the very same thing happened with Italian food in North America, just differently. It changed to suit the local palate and use the ingredients that were easier to obtain or cheaper here. While the original forms didn't disappear everywhere, they were largely subsumed. The revival of some of the more "authentic" styles is in no small part due to modern palates that are demanding them. There was very little desire in my grandparents generation for "unusual ethnic cuisines", even more authentic types of European foods. It was pretty standard North American fare. But my parents generation, and now mine, have had the ability to travel more broadly, and enjoy the flavours of a constantly changing immigrant culture. The latter is a change that hasn't broadly occurred among the Argentines, and probably for a bunch of reasons.
However, locals told me that it tasted way better before the company got sold and changed the recipes.
