It's because you have traded your gold token, they charge fee for holding, if you are not holding any gold token then what's there to charge for?
Take it easy guys. The fee is only less than 0.1% annually, according to the site's notes. 0.1% per year, it does not expensive. For the purpose of the fees, I don't know but the GOLD team can help with explanation.
No hidden fees, free transactions between users and the lowest annual storage fee of 0.99% (0.0027% per day). Yearly storage fee is automatically charged from token holder's wallet by GOLD secure and audited smart-contract, based on Ethereum network, on daily basis.