eli5: Why were some ancient cities like Palmyra and Machu Picchu left to ruin and fall apart over hundreds of years instead of being repopulated?

Question

eli5: Why were some ancient cities like Palmyra and Machu Picchu left to ruin and fall apart over hundreds of years instead of being repopulated?

In: 1677

Answer 1

Lots in here about maintenance and the like. Bigger and simpler answer, they stop being useful. Boom towns around resources, religious centers of religions that fall out of favor, trading hubs when the trade routes move. Cities spring up where there are opportunities and a need for people and when those opportunities and needs dwindle so does the city.