When did you do this? Is this a fixed fee? As Bin mentioned above, your 2nd transfer needs gas and since Ethereum is busy as hell atm, paying $10 or more should be expected since you're interacting with a smart contract, while your first transaction is likely paid with batch transactions. In short, your first transaction is just one of many transactions that likely pay more than $100 or so, but each user get a tx fee and that's why the exchange still makes profits.