Just tastes better
I always used to hate mayonnaise, and couldn’t imagine using it as a regular condiment. Turns out I just hated American mayonnaise.
Japanese mayonnaise is made with rice vinegar and a spice called ajinomoto, which gives it a hint of the flavor called umami. Umami is a special flavor, found mainly in Asian cooking, that can be detected by the human tounge outside the four basic tastes of sweetness, sourness, bitterness and saltiness. Japanese mayonnaise is much better for cooking, especially for making salad dressings. That hint of umami makes all the difference.
Kewpie brand is the most popular brand of Japanese mayonnaise, and so it is a bit of a comfort food like Heinz ketchup is to Americans. Aside from tasting great, it is just nice to see the familiar bottle sitting in the fridge, knowing you can pull it out at any time and make your tacoyaki taste just that much better.