[codesforhugs]

One big factor is simply that a customs authority can dictate whatever process it wishes for ships who want to load/unload cargo there.

It's also not just customs, there are a ton of ancillary processes related to berthing - things like harbor fees, environmental documentation etc.

I know of at least one case where, as recently as ~2015, a shipping company had to keep around old machines with IE8 because that was the only way to interact with authorities at a given port.