There are major inefficiencies in workflow. Way too much picking up and putting down, moving it to one place and then another, stacking, unstacking, and restacking. Then on a truck to go to a warehouse to be picked up, put down picked up and put on another truck to leave the port area. Or on a truck to go to a rail yard to be put on a train.
And that doesn’t even account for the ones that go to a holding area for customs (most don’t).
Unions are a government-provided protection racket. Implicit threats of violence and explicit threats to the economy are expressions of power that could only exist if the unions (not the companies) “owned” the jobs.
If Trump succeeds in bringing manufacturing back, then the longshoremen thugs will have fewer jobs to protect anyway.
The UAW priced themselves out of the car market, but unions never learn. Once you get on the gravy train, it’s hard to jump off.