The explanation would be automation. If we have machines doing the bulk work of food production and distribution (with some people involved, but not the entire population), then there is in theory room for some people not to work. This means other people will need to take up that slack, but lets honestly look at most of the jobs we do and the world is mostly inventing work for itself. "Must see movie?" "Luxury Appartments" "Diamond rings" "Minecraft" etc. etc. Pretty much most of the stuff we buy in the 1st world are luxuries.