People said similar things about facebook, and similar things about Nvidia stock recently (not ipo, but similar "why buy at this price"). Global GDP is over $100 trillion every year, there is a lot of business to do in the world, AI might be able to do a lot, it might be very profitable.

The number might be too high, but doesn't take more than a little imagination and some basic facts about the world to see how it could be worth 20 trillion in 10 years.