In the Middle East especially--with wind and dust--ruins disappear very quickly, literally almost in no time. I had an archeology professor who told us how a dig he worked on, was shut down for the season and when they came back to work on it again 6 months later, it was already half-buried again in dust and dirt. The Middle East is generally a very dry, dusty, windy place....
Wars would happen, palaces burnt or torn down...vacant for a while, covered over in blown in dust & dirt, then someone else comes along, and builds on top of these structures--over and over. One can have 6 or more subsequent layers--and since height is an advantage, new builders never bother to dig out the old underlying structures. This is how the famous "tels" (hills where towns were rebuilt...over and over) in the Middle East are formed.
Jerusalem has literally thousands of years of rebuilding layers over and over each other. Herod the Great's (infamous king of Jesus birth) building projects are still all over--(he was an amazing builder) and 2nd to that, are the Crusader structures from the 1100s. Getting down through all the layers to David's time (3000 years ago) is quite an archeological feat--especially in Jerusalem.
Thank you so much for that explanation. Never thought about it that way.