You don't. But they want to minimize avenues to get sued because people can and probably will file an wrongful termination lawsuit.
I don't know the exact laws, but given California I would not be surprised if there's a "no, you cannot fire someone who's in the hospital over a state of emergency" clause. Similar to how you can't fire an employee to avoid workman's comp.
Yes, I know, and in fact I checked before posting.
I was using “I think” as a conversational affordance to give OP a less confrontational way in to disagreeing with me, if even in an at-will state, termination for cause is better for the employer for some reason (I couldn’t find one when searching, but it’s not an area I am knowledge about).
They don’t. They care about having legal cause to terminate employment, as is the style at the time