This is a problem of most of the stories I have followed, regardless of the medium. But bad TV writers hold a special place on my list.
I got into certain programs because their debuts were brilliant and the characters had interesting personalities. However, with each season, some of the longer-running series have managed to lose me half way. The marks of bad writing include what I have complained about thus far in previous posts, poor character development, the overreliance on clichés or tropes, and poor romantic development. These often overlap.
Awful Writers Will Mishandle Characters
My disinterest in a show is mainly due to how the characters are treated. My biggest complaints aimed at fictional stories thus primarily revolve around character development. Awful writers want to put plot before characters. Unfortunately, any character that is controlled by the plot will soon lose his or her identity. That ruins a story for me. Also, some characters may take over a series that was based more on another character, one family, or even an ensemble.