Crime procedurals are supposed to be rock-solid, ultra-reliable TV institutions. Viewers expect these kinds of shows to be pretty much the same thing, week in and week out, populated by the same set of familiar faces for years on end. Criminal Minds didn't adhere to those unwritten rules, churning out more than 300 episodes despite sporting one of the most active revolving doors in TV casting history.
That lack of stability tends to turn off viewers, as Criminal Minds' downward-trending ratings over the last decade would indicate. Mandy Patinkin (BAU Chief Jason Gideon) left in 2007, Thomas Gibson (Aaron "Hotch" Hotchner) got terminated in 2016, Shemar Moore departed in 2016 and moved on to S.W.A.T., and Paget Brewster and A.J. Cook's characters, Emily Prentiss and Jennifer Jareau, respectively, were written out for a spell. Other actors and actresses who came and went from the BAU: Jennifer Love Hewitt, Jeanne Tripplehorn, Damon Gupton, and Rachel Nichols.
