How are institutional investors buying SpaceX at the absurd valuation?

How are they gobbling up everything elon musk promises spacex will do? such as their AI promises, etc etc. Like, what stops me from making a company, and promising that it will reach a total addressable market of 30 trillion, because i will be selling oxygenated air in bottles, and well, if people pay for water, they can pay for oxygen too. And then i will own like billions of shares of this company and go public, but only offer like 10 shares to the public, so they can fight over it, and increa