If all they did was produce cars, then yes, the valuation wouldn't make sense.

But you're completely ignoring their solar panel and battery production business. Those two things on their own will make them a powerhouse in the upcoming renewable energy industry. Solar panels on residential homes with batteries for storage/backup + utility level solar fields with utility level battery arrays = a massive business on its own.

People make the mistake of comparing them to GM or Ford, when in reality they're the equivalent of General Motors + General Electric.