There's another issue
The IRPCS aka "colregs" require certain things such as a constant lookout. Robots almost certainly cannot legally meet this requirement.
Finally, there's the little issue of automated navigation not being perfect. GPS is very fallible, especially so at sea, even more so when a navy is near. The British Navy blocks GPS all the time in training exercises.
Autonomous shipping makes a lot of sense and I'm sure we'll see it happen in our lifetimes, but there are a lot of hurdles to overcome, which the marketing department at the automated shipping companies always ignore.
Also, the dozen meatbags on a container ship cost peanuts for a company that owns a fleet of container ships. I'd imagine the yearly wage of the whole crew is about the same as one propellor!
Biting the hand that feeds IT
