The dockworker union is too strong.

Exactly. At the pallet level, the equipment to stack, wrap, or receive them are way too expensive. So, humans it is on both parts.

I'll also note for shipping that it's useful to have people to deal with problems caused by port regulators, pirates, and other odd situations.

Per ton, container shipping is roughly 20 times more efficient than old breakbulk shipping methods. So 95% of the labour has already been automated away.