Why? Here's one reason.
Today, I set out to find a couple of new caches in my area, all placed by (let's call him) Cacher A, and failed to find a number of them. When I checked the cache pages upon returning home, I learned that my failure to locate them was not due to my poor hunting skills.
Apparently Cacher A had hunted for one of Cacher B's caches recently, and had left a post with some mild criticism of the choice of sites. Cacher B took great offense at this, and retaliated by going out and stealing all of Cacher A's new caches. He then proceeded to create a new account ("CacherASux") and used it to post taunting notes on each of the removed cache's pages.
Model cacher, this one.