The point of food labels is help consumers make more informed decisions on what food they consume, especially when the food industry works to make food as addictive as possible. Lets not forget that the messaging behind many (most?) products, especially the unhealthy ones, is one of health and nutrition. When the only message about a food is it's health benefits it's not too farfetched that people may consider Froot Loops part of a healthy breakfast. Froot Loops is an extreme example, in most cases it's more subtle, like granola.

It's easier for kids. 'No mama, we already have one sugar point today, a second is too much', 'beurk, sugar, fat and salt!'.

I'm joking (sightly), but it's easy accounting. Give yourself X sugar point, Y fat points, and Z salt point, per day/per week, and you can still eat unhealthy food while making some effort. Small steps etc.