Yeah those ports were designed for a normal nation that ships stuff out too. They were not designed to offload 90% of the Wal-Mart and Home Depot inventory
Oh, please.
Those ports have undergone substantial capacity enhancements in the last 6 years -- mainly aimed at accommodating precisely that import market you've identified (the Alameda Corridor project is a good example of this).
The primary problem with these ports is that they are located in heavily urbanized areas with little room for expansion, and they were originally designed when this nation had a population of about 100-150 million people.