Implicit in your question is the idea that ghost towns might be a notable phenomenon, but I think that you are right to question this. Indeed, small isolated communities that are oriented towards agriculture, some form of resource extraction, or supporting transit between larger communities like the majority of ghost towns in the US are on a pretty fundamental level profoundly unstable on larger time scales. Even looking in places like Western Europe or Japan with traditions of extraordinarily long lived small communities, it is important to consider that what you see is affected by survival bias - the old towns that you see are just the ones that survived.

In thinking about the ways that previously thriving communities end, both in the US and in the ancient and classical worlds, it might be helpful to disambiguate between communities that had access to large and complex markets of bulk goods and communities that didn't. For small communities that did not have access to markets and transport infrastructure capable of commercially meeting food needs, instead relying on subsistence agriculture, crop failures could be a powerful motivator to pick up stakes and seek stability elsewhere. While our Laura Ingalls Wilder-mediated cultural memory of famine as a motivator for the abandonment of small hold farms in the American West might be significantly exaggerated relative to consolidation, generally poor farming practices, and the complex influences of financial and commodity markets - it has indeed played a role. However, for small communities that did have access to bulk shipping in complex inter-regional markets, its those markets as well as the commodities they produced that created precarious communities and then ended them. From garum producing communities like Baelo Claudia in Imperial Roman Hispania to American mining communities like Eureka Colorado, both the sustainability of the commodities they produced as well as the demands of the markets they served were sources of instability.

Outside of early failed colonies such as Zwaanendael, few American settlements have been permanently abandoned due to conflict, however from antiquity conflict would entirely depopulate small communities and make larger ones unfeasible. Thus, perhaps the closest US equivalents to the abandoned ruins of large central cities like such Sumer, Teotihuacan, and Merv would be abandoned indigenous sites like Cahokia?