Because it is made up mostly of fat. It also contains bulk of umami-flavored substances, from vegetable oil amino acids and egg powder to monosodium glutamate. Some sugar and acid. From the side of taste - a solid positive.
But I would not recommend to often eat mazeg from the storage. It is still better to learn how to prepare this suspension yourself, especially if you are a fan of this wonderful sauce. With it, you will get the necessary set of vegetable fats without forcing the body with a dietary dull.
Apparently, you are eating some initially tasteless food. Fresh hot bread tastes better without mayo. A good steak tastes better without mayo. Nuts are tastier without mayo. Chocolate tastes better without mayo. This is quite obvious, of course. From the unobvious - all fermentation products (pickling / pickling) are tastier without mayo, in them the taste has already been strengthened and changed. Legumes and legumes derived from them (such as hummus) also tend to benefit greatly from the absence of mayo. I just can't think of anything that, apart from Mayo salads and trash food such as fries and cardboard hot dogs, would only get better with mayo (without identifying, of course, mayo and tartare, with tartare another song).