They are regulated - their nutrition label tells you exactly how much added sugars there are. You can’t really regulate how much sugar can be in “sauce” before it’s no longer considered a sauce (like subways bread being legally cake) because sauce is incredibly broad and already includes dessert sauces anyway.
It’s added sugar - and yoplait/chobani add a lot of sugar. Yogurt with no added sugar has no more sugar than the milk used to make it does and it is mouth-puckeringly tangy. I make my own yogurt and you pretty much need honey with it to make it palatable with fruit (some people eat unsweetened yogurt without the honey… Those people scare me)