There is a corollary to the old adage "Those who forget history are doomed to repeat it" which goes, "Those who rely on history are doomed to surprise."  Generally, the campaign was over after New Hampshire or so.  The DNC was usually spineless in enforcement.  Well, they failed to make the judgment about history not always repeating itself.  (It often does, though it's hard to say which part of history will repeat itself, i.e., the American Revolution or the French Revolution.  Sometimes, though, something novel happens.)