Corn is a productive asset that generates more corn. Money is not, in and of itself, a productive asset. One of the essential insights of Keynes was that it was possible for real productive capacity (machinery and labour etc) to be idle simply due to lack of liquid money to flow through the system. This was why consumer credit was so crucial to kickstarting modern consumerist economies: like Ford paying workers so they could afford the products, injecting credit allowed consumers to buy items creating jobs to make products, which jobs then allowed consumers to pay off the loans.

"Shortage of specie" has been a real economic problem at times; e.g. https://www.cambridge.org/core/journals/journal-of-economic-...