think you are confusing blockade runners with privateers.
Confederate privateers under a letter of marque are authorized to capture U.S. flagged merchant ships, seize the ship and to sell the cargo and ship. Blockade runners were ships that picked up cargos in Europe, Bermuda, or many Caribbean ports and ran the blockade of U.S. Navy to a Southern port. Much more money to be made selling a cargo load of luxury items than a cargo hold full of blankets for the Confederate Army.
Yes, of course. Thank you for the correction.