Most of the first Chinese immigrants to the US were from Canton / Guangzhou, so most Chinese restaurants were Cantonese. Other cooking styles came later. And the lack of seafood availability in the interior affected what was served, as well.
__________________ May the bridges I've burned light my way.
If you want to see differences in style, look at the Philippines. My husband did several Westpac tours, it took Many, many, recipes to get Pancit "right".
One thing I usually do just for fun is to order bittersweet pork (don't know its english name). If I visit 100 restaurants it will be always different.
My spouse has an uncle and a few aunts that really cook great Chinese food. Very kindly, though, they never make Peking Duck when I visit as they know I had a pair as pets during my childhood and cannot bring myself to eat Duck. I cooked them turkey once and, well, they did not feel it was quite the same.