In the US, we have over-the-air, digital substations such as MeTV and Antenna TV that specialize in airing old shows. Those networks get the rights to old series for fairly cheap, since the audiences on the substations aren’t huge and the shows aren’t in demand from major network affiliates or mainstream cable stations. CBS has made deals with several of these stations to carry shows from their library (the old Paramount TV catalogue). Sony has too (they own the Screen Gems/Columbia library) and they are even an owner of one of the “diginets” (Get TV). Warner Bros has been the slowest of the major TV studios to make its library available to these diginets. I read a story a few years ago that they were concerned about devaluing their library by making deals with these stations. Some of the Warner Bros shows have started to show up over the last few years, but not quite as much as Sony and CBS shows. It also doesn’t help that sitcoms understandably are in more demand, because they repeat better (easier for viewers to take in an episode here an there, instead of a serialized show, where they have to watch every episode to keep up).