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

The long and short of it, is it was abandoned, this means the infrastructure to support it is also gone.
The second reason is that it was forgotten, at least by the people who had the means to repopulate it.
Third reason kinda builds on the first, there was no reason to go back, its easier to build a new city, then to fix an old city.