[Unicron]

Well, everyone in Starfleet has a job with some level of training, even if they don't receive a physical payment like currency for it. And then there are the civilians who maintain things like Earth's environmental systems and research, or even simply want to run a vineyard like Picard's or a restaurant like Sisko's. There's no reason to assume they're idle just because there's not a valuable monetary reward in it for them.