The problem with this analogy is the gold miners are not just trying to mine gold. They are simultaneously doing a bunch of other economic activities that generally make money, as well as trying to mine gold. Some are selling yearbooks back at camp, or putting on plays, or selling food, etc.

nvidia can't make more money than the client companies make altogether, but they certainly can make more money than any(/all) of the client companies make using nvidia's products. It could be the case(and currently is the case) that other non-AI revenue streams are just being handed over to nvidia in the hopes the AI revenue streams take off eventually.