Look at it from the point of view of a merchant ship's crew coming into the Los Angeles/Long Beach port complex. Tied to the pier, with shore power and water connected, not much for the Engineering Department to do. Think "union shop", engineers do not handle cargo. They and anyone else not involved in cargo handling will be going ashore to do things like go out to eat, shop for snacks/toiletries/laundry detergent/clothing/magazines/DVD's and anthing else to get ready for the next voyage.
The Stewards and cooks will be dealing with loading of supplies like fresh veggies with the ship's husbanding agent(s).
All of these people will be interacting with workers on the pier, the security guards, taxi drivers, the cashiers at the supermarkets, etc. Now those people interact with others the same way such as the grocery shopping. If this corona virus is so devestating then does it not stand to reason that most of Los Angeles would be infected by now?