It's easy to get distracted by the value of the transactions, but they're just the payload. Nobody is "buying" a product worth those billions in transactions, the same way someone bought $N worth of books for a bookseller to have $N revenue.

A shipping company is evaluated on its ability to move containers, and nobody cares (well, the insurer does) if the containers are filled with iPhones or cardboard, as long as the customer pays the shipping fee.