the star trek show is about voluntary military service aboard a ship with a strict social hierarchy, it does not represent all life on earth on the show. you don't see every facet of life in the universe on that show either.

replicators give you everything you need and instant travel means everyone is where they want to be at any time of the day and they're doing what they want to be doing. in the future we will figure out how to achieve all this, how to motivate people, basically, without money, we just haven't figure it out yet.