I wondered why Oakland and not S.F. and found this:
There are limited docks that will be able to dock a ship of that size, and the Port of Oakland location was the easiest to seal off, securely move passengers toward their isolation destinations and protect the safety of the public, Newsom's office said. The port is also close to the airport and Travis Air Force Base in Fairfield.
The Port of Oakland's Outer Harbor Terminal also isn't near any big residential or commercial areas, while the San Francisco port, opens up onto the popular Embarcadero, where tourists and businesses are plentiful.
Cornonavirus: California governor explains why Port of Oakland chosen as 'best site' for cruise ship docking
It really makes sense since Oakland is in the East Bay on the same side of the bay as Travis AFB and the somewhat less busy Oakland International Airport. It’s a straight shot of about an hour on I-80 to Travis.