You shouldn't look at Tesla as just a company that sells cars. Uber has a market cap of $64b. If Tesla ever nails self driving, they could turn themselves into Uber almost overnight by deploying that tech to their already sold fleet of vehicles. That obviously isn't a guarantee and I wouldn't even say it the most likely outcome, but even at a low probability it is a possibility that likely adds billions to the company's valuation. There are similar scenarios for other industries with their solar, battery, and trucking businesses.