Why would gold be ‘leased out’?
To make a short-term return on it.
I think that ‘leased out’ is a technical term used in high finance that means "we gave it to China".
To sell it short. I borrow gold from you, sell it and at a later time I have to buy it on the open market and return it to you. If the price goes down I make money from selling high and buying low.
The tricky part is when I just borrow it from your broker/storage company without your permission based on the idea that the broker has enough gold in his possession where if you want it back he can always give you some. Now if more people want their gold than he physically has anymore you might get a run on the bank. That is the house of cards of fractional reserve banking.