We don’t watch a whole lot of new TV because, frankly, we’re underwhelmed by it. (Okay, that’s not entirely true: we do watch Wheel of Fortune and Jeopardy! during the week.) They’ve replaced quality writing with dirty jokes and gunplay. I don’t think we’re the only ones who feel that way, either.
Reruns have always been big business in TV. After four seasons’ worth of shows (80-100 episodes; for most shows, that’s 96) have aired, the series is eligible to be syndicated, where local stations and the smaller and vintage TV networks can bid for the rights to rebroadcast it. Syndication contracts are generally awarded based on the market (e.g. Atlanta, Chicago, Sioux Falls) or the network (e.g. MeTV, Antenna TV, Decades, Ion), and typically run for a one to two years, and there are rules that must be followed as far as who has the right in a market to air the show if there are several entities who have the rights that share the market. For example, here in Atlanta, both a local station (WXIA, the local NBC affiliate) and MeTV (which broadcasts nationwide) had the rights to show The Andy Griffith Show. In that case, the local station showed it and MeTV replaced it with Mayberry, R. F. D. in their feed for Atlanta.
I Love Lucy and The Honeymooners are classic examples of syndication successes. Both were originally shown on the networks (if I remember correctly, CBS and Dumont, respectively) and have been on the air ever since in syndication. Only 39 episodes were made of The Honeymooners and they’ve been playing ever since. I Love Lucy is running somewhere in the world every hour of every day, or so I’ve heard.
There’s another type of syndication called first-run syndication, where a show is created specifically for syndication. Star Trek: The Next Generation and Xena: Warrior Princess are examples of that. But that’s a topic for another day.