But why would you want to buy a company where the valuation reflects an extremely optimistic outcome already? Basically you are assuming obscene growth from SpaceX in AI, datacenters, rocket launches etc just to for the stock to go nowhere. The market cap was over 2T!

When you buy equities, if the company turns out shockingly successful beyond most peoples probable expectations you dont simply want your investment to just stay flat, you want to make multiples of your money. In order to do this, you simply cant start from a 2T marketcap. No company worth 2T can make you 100x your money or even 10x or 5x your money in a reasonable amount of time given the overall size of the economy.

>But why would you want to buy a company where the valuation reflects an extremely optimistic outcome already?

To hedge against the stock going up and making your buy in even more expensive.