I think what happens is that after awhile the arrogance, stupidity, pig headedness, liberalism, conservatism, nit-picking, etc just gets so pathetic that they lose it and move on. Simply disappearing wouldn't be near as entertaining for those of us that chose to stick it out for a little longer, nor as satisfying for those bailing.
Just an observation and for those that'll chose to nit-pick some of the above statement; it is a VAST generalization.