IMHO there are two big reasons for this:
1.) Wall Street has way more money to invest than it can find good investments for. So all stocks are overpriced, but especially “growth” stocks where you just might imagine that the company will expand greatly from its current size. So as a pioneer in the electric car market, Tesla qualifies.
2.) The problem with the idea that Tesla will be able to take over the car market because they have more experience with electric cars than the Detroit automakers is that it is far easier to change powerplants than it is to ramp up from handmade niche car maker to a giant industrial concern.
edited to add: I see that Mangochin has made the same point.
