It's not about sandboxing or distribution, it's about having a regular interface. This is why the container analogy works. In the analogy the ship is a computer and the containers are programs. Containers provide a regular interface such that a computer can run any program that is packaged up into a container. That's how things like Kubernetes work. They don't care what's in the container, just give them a container and they can run it.
This is as opposed to the "old world" where computers needed to be specifically provisioned for running said program (like having interpreters and libraries available etc.), which is like shipping prior to containers: ships were more specialised to carrying particular loads.
The analogy should not be extended to the ship moving and transporting stuff. That has nothing to do with it. The internet, URLs and tarballs have existed for decades.