The Bronze Age burial cairns are monuments to an age of widening social gaps, when chieftains and other persons of power evolved to a distinct group in society, with special privileges such as individual, monumental burials.
A simple rule of history, however, is that people tend to be pragmatic. Thus, these burial sites didn't remain individual for long. The local communities reused them by lifting a few stones and placing urns filled with the ashes of the newly deceased in the holes beneath.
In death we are all equal. History will eventually forget you and your status and deeds, however awe-inspiring they once seemed. This is quite a humbling and refreshing thought.