This phenomenon is because larger ships are more efficient, and ocean shipping is a super competitive, low-margin business (during normal times) like the airline industry, so in order to eek out a tiny profit, ocean lines consolidate and build bigger and bigger ships, which further drops prices. These ships can only actually go to a handful of megaports around the world, though.
Another factor is the infrastructure that exists at the ports - you need to do something with the cargo once it gets on shore. LA/Long Beach has invested in big, efficient terminals for trucks and trains to get loaded quickly and move cargo out of the port in big volumes.
Source: I used to work at Flexport on ocean shipping, so I have a general understanding of the industry
The really interesting changes will be in the ports on the US Eastern seaboard which planned to take advantage of the super-panamax cargo ships dimensioned for the new channel at Panama.
also moving cargo between two ships floating around at sea is dangerous and difficult, giant ships are not meant to hold position parallel to each other in the open ocean (or indeed closely parallel to anything) without the assist of many tugs.
a "geared" (with crane) container ship looks like this, and even so it would be a very risky move to use the crane to do anything other than load a container to/from a wharf while the ship was firmly moored to it.
https://www.google.com/search?q=geared+container+ship&client...
It's relatively dangerous, both ships have to be designed for it, and both crews have to be trained for it.
I participated in many such refueling and replenishing operations while I was in the US Navy.
https://www.google.com/search?tbm=isch&q=resupply%20at%20sea...
This proved not to be able to compete with container ships when they were introduced. The last LASH ships in regular commercial service AFAIK were the Baco-Liners, which served small ports in West Africa and were scrapped in the early 2010s.
This infrastructure would only be valuable or even necessary for perhaps 2-3 months every 5 years.
Who would ever finance that?
... I wish I hadn't