Sugar GDA

I know this has probably been talked about to the end of the world and back but I have a question and thought this would be the place to come.

Basically my goal for the day on here for sugar is 45g, however based on my calorie allowance and also checking the GDA website it tells me that my GDA should be 70g, I know this is obviously from all sugar, not just natural or added but I was wondering why is it on here my allowance is half what is recommended, I don't currently worry about my sugar intake, if I go over I go over but I was wondering if anybody knows why this is the case?