why does my 2007 expedition have no body mount bushings left?

What is your question?

After looking under my newly purchased 07 expedition for the source of a loud nocking when on rough roads. I found that there where no bushings left on the body mounts. why would they wear out so fast. how much does it cost to replace?

What makes this problem better or worse?

when i hit bumps in the road

How long has your 2007 Ford Expedition had this problem?

shortly after i purchased it a couple of months ago.