From this distance it can be hard to conceive of a city being abandoned, leaving usable things behind. But, in a culture using rammed earth (pisé) mud bricks there's little stone to rob and (micro)climate change has been a bit of an a-periodic constant in the nile region, aside from wars. Sand drift covers things remarkably quickly. Scara Brae in the Orkney Islands was engulfed, not a city by any stretch but a settled functional dwelling in a religiously significant culture, abandoned and buried quite fast, if not overnight.