Sugar is not just added to jam as a sinful tooth-rotter, it's also a preservative. It increases the osmotic pressure so that spoilage microorganisms can't grow. The alternative is to cook down the fruit juice to concentrate its own sugars, but that's expensive and it changes the flavor, usually for the worse. In the processing plant, this is minimized by using a vacuum pan, which cooks the fruit at a lower temperature, under vacuum. Kind of hard to find one at your local cookware emporium.
I used to do QA work at a fruit processing plant, during my college years. We made all kinds of fruit goop, according to various customer's recipes. I'd handle hundreds of tons of the stuff without ever tasting any of it. (That was someone else's job.) But the worst was the filling for a prominent brand of "all natural" yogurt. We put two extra sacks of sugar in every barrel. Man, that stuff was corrosive.