What does this mean, really? This always strikes me as snobbery signaling. Perhaps it's traditional, but does that make it "proper?" Why do only some cuisines have such constraints on what is "proper" or "authentic?"
Most “improperly” prepared sushi is not intentionally aiming for something new, but is just mediocre (or bad, depending on your standards), I would guess typically because the chef doesn’t know what they are doing, or maybe because the restaurant is cutting corners to save time/money. Poorly prepared rice is usually the most obvious problem.
Imagine you order a medium rare steak and it’s overcooked and much too salty. If you criticized it you wouldn’t expect someone to say “well maybe it’s not traditional, but don’t be a snob”.
I struggled making that distinction clear when criticizing Mexican restaurants in northern Minnesota. When I would say that I thought a restaurant was low-quality, people would dismiss my opinion saying “sure, it’s not authentic but…“.
However, what I was really saying was that the overall standards of the restaurant were low in terms of food quality and freshness, like fast food or a TV dinner served on fancy plates. In most cases the interpretation of the cuisine was perfectly adequate, and only the preparation and flavor lacked.
The names of dishes (and ingredients) are culinary trade jargon, just like the names of the techniques used to prepare them. In order to achieve unambiguous communication between chefs across temporal and cultural distance, terms like "cacio e pepe" have to be taken to mean one fixed thing—one platonic ideal dish that someone hypothetically made at some point, that all such real dishes are attempts to recreate. Otherwise chefs will just be talking past one-another.
Certainly, you can do things any way you want, and cooks can evolve dishes any way they want. Despite this, terms like "proper [dish]" and "authentic [dish]" still have a use.
A "proper" dish X is the dish that a professional chef expects when they hear X—the culinary-jargon interpretation of the term X. (So: "proper" nigiri sushi is "the nigiri you'd prepare if your practical exam in a culinary academy was to make nigiri.")
As stated above, this is a pretty objective concept; "proper" X will continue to refer to the same exact dish no matter what country you're in, or how long it's been since the dish was invented. (Tweak the dish? New dish, new name. We have a flat global culinary namespace. Yes, regardless of language, because it has to avoid collisions once translated into French. It's much the same as zoology's binomial nomenclature's flat global Latin namespace.)
An "authentic" dish X is the dish that a chef conversant with the culinary heritage that originated the dish X, would make, if you ask them for X. (This is not to be confused with authenticity of ingredients. A Ukranian immigrant making borscht with American beets is using inauthentic ingredients to make authentic borscht.)
(Amusingly enough, often an "authentic" dish X is the least "proper" X, because the dish has evolved in its cultural homeland since it was invented, and so the global culinary profession's concept of the dish has diverged from its homeland's evolving conception of it. The avant-garde and the authentic can overlap. But the avant-garde cannot, by definition, be "proper.")
...and then there's the term "traditional", which just means for a dish X that the chef who made the dish is a traditionalist—nostalgic for some bygone era (where the era they're nostalgic for is left unspecified, can change from chef to chef, and can change over time!) This term is, by contrast, pretty useless. Saying "give me a traditional X" is kind of like saying "give me a [git ref HEAD~1] X." Might work for you now, but won't work later. Chefs don't tend to use the word "traditional" much. (Instead, they'll speak of a culture having a particular culinary tradition, but will identify a specific period of that tradition if they want to pinpoint a particular dish they want to make.)
I think it's important to recognize that the degree of precision required to achieve "authenticity" varies between cultures.
Italian dishes tend to be extremely precise in terms of what ingredients may be added, to the point where many people would disagree you're making an authentic Carbonara sauce if you add garlic to the sauce, or even use pancetta instead of guanciale.
On the other hand, a culture like the US usually only requires that dishes follow a rough template - a meatloaf is a meatloaf provided it's predominantly ground meat molded into a loaf shape and baked.
It may sound "snobbery" to some, but there are important distinctions to make between the levels of how well something is prepared. The two most important being "proper" and "improper". Burnt rice, rotten meat, and missing ingredients are definite examples of "improper".
And cuisines can definitely have constraints on authentic, e.g. hard shell tacos, while delicious, are definitively not "authentic" Mexican. Just like adding spices to my grandmother's (or my) chai is an easy way to lose your head.. it's just not right. Would you like it if your salad resembled more a pasta? Or if you were served pizza as a mixed vegetable platter?[0]
I don't think parent^3 was being a snob because he wasn't describing a wine as being "better" because it tastes "oaky". A statement like that is probably deserving of hate, because what does oak even taste like?
derefr has a great explanation of traditional vs proper vs authentic. But on Why do only some cuisines have such constraints?, that's probably just down to culture.
Prescribing how a dish is made expresses a deep cultural identity through food, even if that food has evolved greatly over time. You might be able to change a dish and even improve its flavor, but it would no longer be that culture's food.
Now, why do only some cuisines seem to be sticklers more than others? Probably because some people are more sensitive than others about their food. They probably went to get a certain kind of meal, and it wasn't what they were expecting, and they were pissed off. And I get that. If you have an intention to eat this culture's food, you don't want some weird western "interpretation" of it, or some jackass from NY who thinks putting cream cheese on it makes it "regional". You want to be connected to where that dish first came from, and all the breadth of history that distilled into creating its specific flavors and textures. You want that dish.
It doesn't help that when dishes are transported out of their country of origin they get transmuted into some kind of local monstrosity. Tex-mex? Spaghetti and meatballs? "Chinese takeout"? California rolls? It's clearly not the real mccoy, but people still call it "mexican", "italian", "chinese", or "sushi", when it barely resembles those cuisines at all. And don't get me started on trying to find a real burger or bbq anywhere outside this country, to say nothing of those rarer American foods, like drip coffee.
And to be honest, there's probably a certain amount of cultural elitism involved in "cuisine" (the French word for "we're better than you"). I've always found the French and Japanese alike in that they both think they're superior to everyone else on earth. That's probably going to result in a lot of uppity people wanting their dish the "superior" way. But for me, it's about wanting to understand and respect the deep cultural traditions that produce singularly unique and beautiful expressions of food.
Yes, coffee is made in many different ways around the world. The French, for example, only drink drip coffee at home. The Viennese famously have it strong with whipped cream. Much of the Mediterranean uses an Ottoman-derived concentrated boil method. Trying to find a drip coffee in these places, and many other countries, can be quite difficult.
What does this mean, really? This always strikes me as snobbery signaling. Perhaps it's traditional, but does that make it "proper?" Why do only some cuisines have such constraints on what is "proper" or "authentic?"