According to the FDA website, no daily reference value has been established for sugars because no recommendations have been made for the total amount of sugar to eat in a day.
Keep in mind that the sugar values listed do not distinguish between naturally occurring and added sugars because it is not a chemically meaningful distinction. So unlike nutritional information about vitamins, proteins, fats, etc, there really is no level of "recommended sugar" that would make a good blanket statement for everyone.
Claims that high consumption of added sugars harmful to your health is an extremely complicated subject. It's not that the sugar itself is inherently harmful due to any of its chemical properties, it's just that added sugar tends to be in products that have extremely high fat and high calorie content and are easy to consume in large quantities.
So saying to avoid foods high in added sugars is good general advice, but labeling products to indicate that you should consume {x} amount of sugar per day was not a piece of nutritional guidance the FDA was prepared to make in that labeling.