Exactly this. While valueing companies on future growth makes sense, Tesla's current evaluation is bigger than the 10 largest car manufacturers by market cap after combined [1]. That kind of implies that people think Tesla alone will be as profitable as these other ten combined, which just seems like a totally crazy bet to take. Tesla would have to take over huge parts of their market share while keeping high margins on expensive cars. There isn't so much population that is able to spend 50k or 100k on a car.

[1] https://companiesmarketcap.com/automakers/largest-automakers...