Corby Kummer explores it:
Taking out sugar is hard. As with sodium in soups and fat in breads, sugar is not just for taste but also plays a functional role, affecting a food’s texture, color and bulk. Home bakers know that it’s often harder to cut down on sugar than butter or shortening, and so do cerealmakers. Cerealmakers’ strategy is to move sugar from the inside of cereal pieces, as they’re called, to the coating, and to rejigger the sugar’s crystal size—all to increase the sensation of sweetness while reducing the actual weight of sugar used. The problem is the “bowl life,” a term I loved upon hearing—how long before cereal in milk gets soggy or slimy. General Mills wants three minutes of bowl life.