Well, how many people in the 24th century have jobs? Maybe most of the human population, or even most of the Federation's population, are idle. There must be a reason humans don't use currency-based economics. Maybe it's the replicator. Why do the Ferengi have jobs, then, if they have replicator technology, too? Maybe it's purely cultural, with latinum as a useful way to keep track of who is "winning" economically.