It depends if the creators of the show are targeting syndication. Star Trek is a good example of this - TOS, TNG, Voyager episodes are generally self contained

It depends if the creators of the show are targeting syndication. Star Trek is a good example of this - TOS, TNG, Voyager episodes are generally self contained and single episode reruns are viable. DS9 on the other hand had more long-running arcs requiring more context, making the syndication rights less lucrative. Rarely did reruns of DS9 air after the series ended.