Europe also quickly underwent large scale depopulation when the western roman empire collapsed. That's how civilization collapse works. But in both cases these were isolated events, there is no such trend. Cities like Cholula have been continuously inhabited for over 2000 years. How long people remain in an area depends on the geography - in arid valley environments like mesopotamia or central mexico, both cities and civilizations tend to only last a few centuries as river patterns change, resulting in droughts and migrations, and a lack of natural barriers makes invasion common.