The creator/showrunner leaving its show is common these days. They usually have an idea on where the show is going, but then, the studio or network will want a procedural or stories that wraps in 42 minutes so it's easier to sell them internationally, there are disagreements, the showrunner signed options with the studio to develop other shows, so they take that opportunity.
Your thread may be a coincidence, as a french-language journalist had a similar topic on his yesterday's column.
Si vous comprenez le français : http://plus.lapresse.ca/screens/4c5f...6068%7C_0.html
Journalist is reffering to the expression Jump the shark: "Jumping the shark is an idiom created by Jon Hein that was used to describe the moment in the evolution of a television show when it begins a decline in quality, signaled by a particular scene, episode, or aspect of a show in which the writers use some type of "gimmick" in an attempt to keep viewers' interest. The phrase is based on a scene from a fifth-season episode of the sitcom Happy Days when the character Fonzie jumps over a shark while on water-skis."
http://en.wikipedia.org/wiki/Jump_the_shark
Then he takes examples such as Dallas (the Bobby Ewing resurrection), True Blood, wondering when exactly the show jumped the shark, Roseanne, when they won the lottery, Felicity when she cut her hait in season 2, Lost, when Eko met the smoke monster (3rd season), Weeds after the 3rd season finale fire, or The O.C. when Marissa shot Trey in slow-motion only to get shot a few episodes later.
Some of these shows experienced a big drop of audiences after their stunts or bad decisions, some others just retains big audiences but multiplied their sillyness, but why are we still watching, torturing ourselves, are we masochists or just optimists for a super finale ?