There is no cash. The price of a stock is just the price the last guy who bought one paid, and does not represent what the company is worth. I suspect (but am to lazy to find out) there isn't even enough money in circulation to buy all companies at current stock price. AI companies take this to the next level, their companies valuation is already based on nothing, and they promise to buy stuff for large amounts which is taken at face value because the company is worth a lot.

It's basically owning one hundred euros, selling one eurocent for a hundred dollars to someone and suddenly everyone believes you're a millionare, so now you can borrow lots of money since you're good for it being rich and all.