Too Much Free Time
That is not a slam of the hundreds of EverQuesters who devoted days to killing off one supposedly unkillable monster (although you do kinda wonder), but the basic problem for any central entity trying to cope with a very distributed computing network. Anything you build will face tens of thousands of man hours dedicated to taking it apart.
In this case, EverQuest's owner Sony thought that merely giving a monster 100 billion hitpoints would make it immortal. What it did was make it a target. This Kerafyrm effect should be studied at the nation's great universities.
(via Fark.)