[mrpopo]

Fruits are lacking vitamins and minerals, not sugar. In fact, the carbohydrate content in fruits is increasing with increased CO2 concentrations (explained in the article).

Anyway, the reason why this is a problem is explained in the article.

“As many as three billion people around the planet, most of them in low- and middle-income countries, cannot regularly afford a healthy diet, and at least two billion are suffering from so-called hidden hunger, missing key micronutrients in their diets,” Sova says. “These people cannot afford additional nutrient declines in plant-based foods.”

Nutrient deprivation isn't just scurvy and rickets, it is also linked to many behavioural and long-term health problems.