1. The network is airing reruns to fill time. If there is a gap in the programming schedule, the network may choose to air reruns of a popular show to fill the time until new episodes are available.
2. The network is testing the waters for a potential reboot. Sometimes, networks will air reruns of a popular show to gauge audience interest in a potential reboot. If the reruns perform well in the ratings, the network may decide to move forward with a reboot of the show.
3. The show is on hiatus. If a show is on hiatus, the network may choose to air reruns to keep fans engaged with the show until new episodes are available.