Perhaps I just don’t want to know

I keep hearing and seeing ads for “Juice with a full serving of vegetables hidden in every 8 oz.glass”. Or “a full serving of vegetables hidden in a spaghetti or mix with ground meat sauce”.
First, why hide it?
Second, what was in there before if not the juice of some plant?
Third, am I supposed to be too daft to know that a tomato based product such as jar sauce has tomato and vegetables in the first place?
Last, what is in there to mask the flavor of the juice or vegetable?