Why are archaeological sites buried?

well, because dirt blows from one place to another, and different things happen... earthquakes floods, etc, that all move dirt from one place to another. Over time, whole cities can be buried, and new ones built on top. Dinosaur bones and other things of arcaeological interest all get buried... or eroded away, washed away, and buried somewhere else. So, when we want to look at things from a long time ago in history, we usually have to dig them up.