Often stations won't run the later seasons. I've read a few will try to sneak later season episodes in to the rotation by running them in Black and White. When TBS had the show, they ran only the early seasons weekdays in prime time and the later seasons in the off-hours on weekends. It was a classic show that turned into another mediocre 60s sitcom. What happened?
Many people point to the loss of the Andy-Barney chemistry. I don't think that was the controlling factor. Even early on, Barney did not appear in all episodes in a given season. Some mention black and white giving the show a timeless quality. I think the problem was a different writer and producer who just didn't get it. They weren't writing for Mayberry, they were turning in BS that could have been submitted to any number of shows (and with minor changes, probably was). These people just didn't realize Mayberry was the star and they didn't appreciate the appeal to an idyllic small town (where everybody knows your name). They also got rid of the recurring characters which gave the show its flavor and texture, the ones people today remember: Otis the drunk, the pretentious mayors, the old maid sisters who ran a still, Ernest T. and the Darlings, the money grubbing store owner, the choir director who managed the hotel. And they drifted away from the premise of most early season episodes: A flawed big-city stranger comes to town and is redeemed by the experience of Mayberry. A new deputy to whom Andy could play straight man would have helped (not another actor reading lines written for Don Knotts); like MASH and Cheers later on, they should have brought in somebody who would offer a marked contrast to the character being replaced.
Many people point to the loss of the Andy-Barney chemistry. I don't think that was the controlling factor. Even early on, Barney did not appear in all episodes in a given season. Some mention black and white giving the show a timeless quality. I think the problem was a different writer and producer who just didn't get it. They weren't writing for Mayberry, they were turning in BS that could have been submitted to any number of shows (and with minor changes, probably was). These people just didn't realize Mayberry was the star and they didn't appreciate the appeal to an idyllic small town (where everybody knows your name). They also got rid of the recurring characters which gave the show its flavor and texture, the ones people today remember: Otis the drunk, the pretentious mayors, the old maid sisters who ran a still, Ernest T. and the Darlings, the money grubbing store owner, the choir director who managed the hotel. And they drifted away from the premise of most early season episodes: A flawed big-city stranger comes to town and is redeemed by the experience of Mayberry. A new deputy to whom Andy could play straight man would have helped (not another actor reading lines written for Don Knotts); like MASH and Cheers later on, they should have brought in somebody who would offer a marked contrast to the character being replaced.