I don't think there are any humans picking up and moving these containers by hand. Robots are already doing the physical moving from one transport type to another.
You'd be surprised how strong the longshorman's union is. It's a cesspool of nepotism and corruption(at least in San Diego, where I used to be close to a family of them and got to hear the dirt). It would take a major economic catastrophe(no, not like the current one) to displace them, and you can bet there will be violence in return.
At the California ports experiencing the worst of being unable to fulfill high demand, the robotics space is intentionally diminished by union activity. Rotterdam stores, moves, and transfers with much greater efficiency with robotic assistance.
However, I don't support injuring workers with tech efficiency advances - it's morally wrong.
But I do wish tech and labor everywhere had better discussions on how to introduce efficiency while also, and more importantly, preserving gainful employment and creating better work experiences.