There were critics of his arrival on the show, but his character grew on me. I thought it opened up a lot of delightful plot developments, and the actors rose to the challenge. Alas, they began the same ridiculous romantic games with Veronica and Silver's Alec, and soon I found myself forgetting to watch the show. I peeked in now and then, and suddenly Ron Silver was gone, and the most insulting cast addition yet had arrived. A Marilyn Monroe clone.
Writing is one of the biggest factors.
Often as soon as the original writers pack their bags, the show goes straight down the toilet. An important cast member moving on to greener pastures, in a bigger show or in movieland, can also be a disaster. Ratings-hungry executives can be the most devastating, reaching in and stirring things up on a perfectly good show. Some programs survive the trials. Many good shows have died an anonymous death this way.