Why or how would anyone think making cars at this point is an "essential" business?
Argue what you will but trying to argue that point sounds crazy to me.
If the law says I owe 40% of my income as taxes, it doesn't allow me to question whether the law makes good sense or is fair, I just pay the 40%. Likewise, if the law defines my business as an "essential" business, I don't question the law or whether it makes sense, I just follow the law as intended.
Let's look at what the law actually says:
"i. The minimum necessary activities to maintain the value of the business’s inventory, ensure security, process payroll and employee benefits, or for related functions."
The business's inventory consists of auto parts and assembled vehicles. Because car sales of all brands are allowed to proceed under this law, Tesla has a right to replace the cars it sells to maintain the value of its inventory. Apparently, the sheriff would not make a good lawyer or Judge which is not surprising because he's not trained as either.
However, the order does prohibit Tesla from making significantly more cars than it sells. Or stockpiling parts in excess of what it needs to build cars to replace those sold. I don't see either of these limitations as being a problem unless Tesla can't sell every car it can make. Because in that case it could be helpful to stockpile certain parts or even entire cars to a limited degree.