One guy, on foot, steps out from behind the bus stop, jumps the queue, and once he steps in, he pulls out a gun. A mere lone pedestrian has now succesfully comandeered a large bus full of people.
Same principle. All you need is to catch up to the sitting-duck commercial transport and ask the skipper whether he’s willing to get his ship and people shot up for the sake of merchandise.
It was mentioned in an earlier post but it is something that people tend to overlook: a commercial freighter has a very small crew, compared to a ship where there’s people aboard who have to do work other than merely drive it and put out a small fire/leak before it gets big (e.g. a fishing vessel, passenger ship, or military vessel). Cargo handling is now mostly containerized and done mechanically in port by a shore-based crew; most ships are powered by quite reliable diesel engines that are NOT required to put out high performance on demand.
So there’s not a large contingent, and merchant seamen are not Marines trained to repel armed boarding parties. Merchant vessels are NOT armed for that purpose, so all it takes is a very small band of well-armed, motivated attackers.