I was explaining this to my daughter in quite simplified terms the other day- we evolved to taste sugar and enjoy it because finding a sweet edible plant meant we had a source of energy to help us hunt that day. Pretty useful if you're a hunter-gatherer.
So we seek out sugar. Now we can get it whenever we want it, in much more massive quantities than we are supposed to be processing. Most of us are addicted. I'm not an exception.
It's not necessarily the companies in this case at least not for the tomato sauce.
It's deceiving how much sugar is also in natural, unprocessed and healthy foods.
According to Google there's about 2.6g of sugar in a 100g tomato, and it takes roughly 2200g of tomato's to make a jar of sauce the size of a 680g jar of ragu, which according to their nutritional facts has about 43g of sugar in the jar, whereas the raw tomato's themselves would have contained about 56g of sugar.
It takes a lot of tomatos to make pasta sauce. Even a little sugar in one tomato adds up quick.
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.