Sometimes things may happen like creative differences, somebody gets sick or dies, somebody just gets tired of the role, an actor gets into trouble etc. It just seems like show creators nowadays just refuse to recast a character even when it would make things simpler. The actor that played Carl on the walking dead wanted to pursue other interests so they kill off Carl instead of recasting him. Jussie Smollet became the first black man to fake his own lynching so they give his character on Empire the Judy Winslow treatment. I haven’t watched the Chi yet but from my understanding they killed off two key characters because of behind the scenes issues and now fans say the show is not what it use to be. It seems like old shows had no issues in that regard. “the role of _ will now be played by _”.