It's mostly not survivorship bias, actually, and the ones that remain haven't been continuously maintained over the centuries. Many of the ones still standing t

It's mostly not survivorship bias, actually, and the ones that remain haven't been continuously maintained over the centuries. Many of the ones still standing today suffered from centuries of neglect, damage in war and rebellion, and even were actively looted for materials to build other buildings from. Others just got gradually buried by floods (or volcanos, etc) and are intact underground.