Yeah but in reality, most cargo thefts are replacements, not outright thefts. The item in question is replicated with a dummy item and the proper exchange is none-the-wiser. However, that's why a corp would own their own port, and routinely send in operatives to weed out bad authorities. Sure they can play the bribery game in neutral or rival corp ports, but over-time the corps are going to prioritize hiring loyalists rather than buying loyalty. Eventually theft like this requires lots of planning and coordination, a level of stealth would be required then.
But then again, having been hired to find and report bad interests for a corporation in RL, maybe this is my experience over-riding the canon. Perhaps Corps are too big to hire loyalists or lack a level of direct management available to ensure loyalty. But then, you can buy off truckers, ports, and outright thefts become a viable problem.
Then again, I work in a warehouse distribution center right now. I proposed the organization audit each shipment in random days and ensure shipments are done right. You would've thought I was suggesting that they hired crooks or delinquents. I am temping in place where the business has had very costly shipment mistakes and disappearances. Unlike politics and government, most businesses don't want to fund the bad guy division known as auditing. It's a surprising acceptance of inefficiency to me. I think MegaCorps, if they truly sought profit would avoid this inefficiency at any cost because it can shut their entire flow down, or at least a major lane.