You also include Tesla in the suit to make it harder for the driver to weasel out of it by blaming Tesla. Best case, jointly and severally liable and you can execute the judgement against the party with money or assets to seize. More likely case, Tesla actively helps your attempt to get a judgement against the driver.
But, look at it from the lawyer’s point of view: Tesla has more money. If you include Tesla in the suit, they may pay you to go away.
You also include Tesla in the suit to make it harder for the driver to weasel out of it by blaming Tesla. Best case, jointly and severally liable and you can execute the judgement against the party with money or assets to seize. More likely case, Tesla actively helps your attempt to get a judgement against the driver.