Curious about the low calorie count of berries

I've been tracking my food intake on this portal and noticed berries like raspberries and blackberries are listed as extremely low calorie, sometimes just 1-2 calories each. As someone trying to eat healthier, this seems too good to be true for how sweet and satisfying they are. Does anyone know the nutritional science behind why berries are so low calorie compared to other fruits? I'd love to understand it better so I can incorporate more berries into my diet plan.