It can be automated it would just never be worth the cost. Every ship is different and has its own requirements.

If they were all 100% exactly the same, using the same hardware in all the same places then it would be cost effective to automate their disassembly. Otherwise every single ship is a one-off edge case.

Even if they're mostly the same many will have had upgrades, repairs, and changes over time that could literally throw a wrench (that someone accidentally left inside an interior area) into the whole (automated) operation.

I think the best case scenario is to enforce shipbuilding standards and deny ships entry if they don't follow them (for loading/unloading, anyway). Then you setup standardized dry docks with robotic arms that are already preprogrammed to disassemble these standard vessels. They may need human guidance for some areas that are allowed to be non-conforming but as long as the majority of the ship adheres to the standard it'd make the whole process much smoother and more environmentally friendly.

From an environmental standpoint the real issues from these vessels isn't even the difficulty of (environmentally friendly) disassembly. It's their emissions over their working lifetime and super toxic things like anti-fouling coatings that where we have no good way to remove or dispose of them. Like, even if you rip off the outside of a ship what do you do with that toxic waste? It's nasty stuff.