Neat - For neat stuff you found

It’s mayonnaise that has been thinned with water to lower calorie content. To regain an appropriate texture they add mustard powder and modified cornstarch. To offset the “tang” from the vinegar and mustard powder they also add sugar (via high fructose corn syrup)

There is also the possibility that something within “natural flavors and spices” contributes to texture and mouthfeel but that is a mystery protected by vague labeling and valuing trade secrets over potential allergen information and properly informing consumers

As a result it is not mayonnaise but more akin to a salad dressing. Many salad dressings start out as a mayonnaise but we don’t call them that anymore once you add a bunch of nonsense that makes them taste wildly different

A more interesting question is why is kewpie so different from hellmans/dukes/insert other American mayo? They are all definitely mayonnaise. The short answer is that kewpie only uses egg yolks, rice vinegar, and adds msg and some spices (probably pepper and garlic), whereas American mayos tend to use whole eggs, white vinegar, and no msg or spices. Otherwise the ingredients are fairly similar (sugar, salt, oil)