I’ve seen several threads where chefs confess that all they do to make their dish(s) popular is load it down with butter and sugar.

Not “confessed”. That’s a part of what they teach in culinary school. Restaurants strive for increased flavor, and the most effective flavor profiles are sweet and umami. Sugar and butter (or meat or MSG etc).

But yeah, we definitely use more sugar (instead of, or as well as umami) in America. However, there’s a lot of that going on in Japanese and Chinese (real, as in eating in China) cooking as well. When I was in China, everything that wasn’t meat was shockingly carb-loaded. These weird (yummy) sweet cheese breads I swore had simple syrup slathered all over them with what tasted almost like American Cheese.