Aha! It's because we are talking about the value of a laborer, of a plebian, of an everyman. The value of the typical person, to some society, is the labor that they can provide to the society. Money is the only way that society can estimate the value of people. This might be a foreign way for you to look at people, but it's common in the Marxist worldviews.

In other words, society doesn't care what you're doing when you aren't working, as long as you're leaving society alone. Thus society has no real reason to pay you just for existing. We might demand that our society put money in everybody's pocket, as a way of creating a capitalism which respects humanity, but it is not strictly necessary, because money is not strictly necessary for a society to exist.