Tesla was found partially liable for this crash. The reason they were liable was they sold something claiming (practically speaking) that it could do something. The customer believed that claim. It failed to do that thing and killed people.
So the question then is - how much did Tesla benefit from claiming they could do this thing? That seems like a reasonable starting point for damages.
And the fine needs to be high enough to prevent them from just saying - oh, well, we can make money if we keep doing it.
If you could only fine a person for committing murder, you wouldn't fine a billionaire $5m, and then hope he wouldn't go on killing everyone he thinks he'd rather have dead than $5m.
So the question then is - how much did Tesla benefit from claiming they could do this thing? That seems like a reasonable starting point for damages.