Because that show still has value. Just because they aren’t making money on it at the moment doesn’t mean they never will. A prolific celebrity like Betty White passes away, and there is increased interest in TV shows she did in the 1950s no one cared about before.
Also, they are almost certainly showing it somewhere. There are dozens of streaming services out there, not to mention broadcast TV. With the advent of digital subchannels, there are dozens of broadcast networks and hundreds of TV stations looking for syndicated content. Almost anything you would want to watch is probably being shown somewhere or somehow.
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