Why do some Italians who were born in Italy, but currently live in the states, make fun of the way Italian-Americans cook their food?

I've eaten both chicken parmesan and spaghetti and meatballs, even though Italians in Italy don't eat that.

I've also eaten Italian food that you won't find in Italian-American restaurants. I speak and understand some Italian, so I'll hear native speakers from Italy sometimes criticize the ways Italian-Americans cook their food, and say things like merda or vomitare cibo meaning $__t or vomit food.

To me it's disrespectful, because most Italian-Americans preserved their heritage as much as they could, just like other ethnicities.

Yes sure some of the food that Italian-Americans cook isn't related to the way Italians in Italy cook their food, but so what? 

Italians from Italy don't realize, that Italian- Americans and their ancestors, had to add certain ingredients in their food that didn't exist in Italy, and a lot of Anglo white people that went to Italian restaurants back then, ate food that required a lot of starch and meat, and that's when spaghetti and meatballs was invented, they had to pay the bills.

Sometimes Italians from Italy will complain about how Italian-Americans overcooked their pasta, and put too much garlic and sugar in their sauce, which is not always true. If anything they should try to help these people.