Just one possibility. The pirates have the resources to escalate. Whether or not they will, and whether or not piracy will remain profitable if they do escalate remain to be determined.
You’re right: I don’t know how they could move the cargoes and ships if they couldn’t ransom them. But given their organization, I wouldn’t be surprised if they started hiring brokers...
Brokers don't have much interest in food, clothing, or electronics that are saturated with salt water. If the pirates escalate to bigger weapons, they're going to be letting water flow to the wrong side of the ship's hull, and the cargo will be worthless. I think forcing them to escalate to a shootout with a real navy is an excellent alternative compared with paying them for committing piracy.