That kind of armament, and the staff needed to operate it, is incredibly expensive. Even if scaled down to commercial-audience models. Even when compared to the cost of huge-displacement cargoes.

Not saying it’ll never happen, just that it’s a much more costly proposition than some might think.

And that’s before we get into the numerous second order issues. Crewing an armed ship suddenly requires very different HR practices. Parties interested in stealing one may now include much more developed military actors. Mooring a container ship across from an LNG terminal is low-risk. Mooring that same ship with medium range weapons may be outside the risk envelope of lots of ports.

Costly is relative. I’m sure Samsung could adapt the border-protection auto cannon turrets that they’re already producing in the thousands to ward off invasion by NK.

It’s a gun, on a turret, with some electronics.

It’ll be a thousand times cheaper than losing the cargo.

It’ll reduce insurance costs and “pay for itself” after just a few trips.

Speaking of which, a turret isn’t single use! It can sit there with minimal maintenance for dozens of trips, protecting tens of billions in cargo over its lifetime.