The poor have their needs met. Once you reach that level, why spend precious leisure time just to become marginally wealthier?
So that when you are too feeble to care for yourself, you can afford care that doesn't involve turning you into a blob by overfeeding you or conveniently killing you off with a negligently spread staph infection after years of soul destroying institutional care by the embittered and underpaid. Becoming marginally wealthier than poor wouldn't do this, but I suspect this is the real goal of most 9to5for40 life plans in the US.