Screenwriter John Rogers believes TV writers have "a fundamentally different relationship with story than film writers do."
This difference between TV writers and film guys is pretty common,
actually. As one of the relatively few guys who flips back and forth I
think this is because in film, a plot’s something you move your
characters through to change them. In TV, generally, your characters
inhabit the plot, but don’t really change.
That’s true, for the most part. People want the same show, only different, every week. No matter what trials and tribulations they endure, they will, in the end, be the same person they always were. Captain Kirk was the same guy at the start of his five-year-mission as he was when cancellation came in year 3. D.A. McCoy on LAW AND ORDER may be getting older, but his character hasn’t evolved. Matt Dillon got craggier over 20 years of GUNSMOKE but he never changed…and neither did his relationship with Miss Kitty. Gil Grisson on CSI is the same guy he’s always been…even if he went through the mini-ordeal with his hearing loss.
That said, we’re seeing characters change and evolved with thee narrative arcs built into shows like DEADWOOD, SOPRANOS, THE SHIELD, BUFFY and NIP/TUCK. But I would argue that most of the characters on primetime network shows are still pretty much locked in place, even in shows with an arc.