Why not?

A lot of people aren’t putting many miles on their vehicles while all this is going on.

A lockdown that keeps Tesla closed is going to reduce demand for new cars for related reasons.

Driving is only down about a third from pre-pandemic levels.

But more broadly, we can't centrally plan which things people do or don't need over the long term. It just isn't an effective economic strategy.

But this isn't long term. A few months is a far cry for long term.

A few more months isn't going to give us a vaccine so at worst that's just causing more economic damage, leaving hospitals empty and moving the pandemic two months into the future. At best you open back up with safety procedures, and limit the spread. But there's no reason you can't do that exact same thing today.

Also, I agree with Musk that an indefinite lockdown is unconstitutional. And if it's not, I want our laws changed so it is. It may be a good idea health-wise (or may not, see increased suicides) but that doesn't make it legal and letting an unelected official impose an indefinite lockdown is just bad policy. So if the local authority couldn't give a deadline, I'd tell them to piss off too.

It seems even more implausible that the risk will be less in a few months than in a few weeks. What’s going to change?

We’ll most likely have contact tracing and a good supply of tests in two months. As well as lot more ppe.

So a lot will be different in two months.

Alameda County already has contact tracing, a lot of tests, and sufficient PPE for ongoing needs. (They admittedly don't meet the state standards that every hospital should have a 30 day stockpile.)

Isn't Tesla the only car manufacturer with no reopen date in the next couple of weeks?

It won't stop being a risk until we have a vaccine, but the risk may be smaller, and once the risk gets small enough we may be able to keep it that way through testing and contact-tracing.