It actually is. Except it's not added between growing and fruit and consuming it, but before growing the fruit. Fruit have been bred and genetically engineered for high sugar content for millennia.

... none of this is to bash fruit - they are definitely a much better alternative to sugary drinks and even fruit juices, due to their low glycemic load. But still, it's important to remember that fruit, especially some fruit, are far from being sugar free.