It is hard to know what the heck is causing it, but some have said California trucking regulations and the fact that China owns controlling shares in the large West Coast ports might have something to do with it.
For most producers that have a monopoly cutting supply does drive up prices and makes customers pay more, and China holds a virtual monopoly in many manufactured goods.
China also owns the production of Ocean containers and truck chassis - without these, Ocean shipping is impossible.
I have seen claims that in addition to CA laws that reduced the number of trucks hauling from CA ports, shippers started refusing to load containers on the return trip (so they did not need to wait for them to be unloaded in china). This then jammed the ports as they literally had nowhere to put the containers that come off of the ships. I also suspect that their inventory management system broke down.