I looked it up a little more. There's a clause in the longshoremen's union that forbids certain uses of automation, as a form of job security. Nowadays, it's possible to make the entire port nearly 100% automated. Those shipping containers can't be lifted by hand anyway, they have to use a crane.

If I was representing the employer, I would make a "no layoffs until retirement" promise to the union in exchange for allowing automation. In the long run, it's cheaper to use automation and just pay off the workers for the rest of their lives.