Wealth is not in fact finite. If you take a piece of lumber and carve it into a dresser you've just generated wealth. Resources kind of are but not really, extraction takes it from unusable to usable and essentially creates it (also, trees literally grow out of the ground). Similarly Tesla has made a lot of cars that people drive and AI companies have created products that have hundreds of millions of DAU.

Whether that "justifies" the market prices is orthogonal, all the market price says is that people want to own a piece of the pie at the current price being offered. It can stay that high as long as there continue to be people interested in owning shares of the companies.