So if we have a distributed Galt's Gulch (e.g. some expensive towers in NYC and SF), how does that change things? How does a rich person owning a brownstone on

So if we have a distributed Galt's Gulch (e.g. some expensive towers in NYC and SF), how does that change things? How does a rich person owning a brownstone on my block prevent me from selling my labor to other non-rich people? When you discuss rich people owning inner cities, those inner cities have value because people want to live in them and have resources to trade for the right to live there. In this hypothetical dystopia, no one will have any resources to trade for living space, so those inner cities will become valueless. (Or perhaps the rich will enjoy walking through uninhabited cities.) There is plenty more land available at low cost in other locations - Detroit, Kansas, etc. What prevents the non-rich folks from building their own industrial complexes and inner cities in those locations? The rich and their robots can entirely occupy the abandoned city of Manhattan, but what prevents non-rich people from buying up $5,000 houses in Detroit and building a new utopia there?