Mannix didn't make it as far as Hawaii Five-O did in seasons, being canceled at the end of 8 years. Mannix was renewed for a ninth season. However, ABC got the rights to air the reruns of Mannix and CBS felt they might lose viewers who will switch over to ABC to watch the reruns instead of new episodes, so they pulled the plug. Hawaii 5-O was not losing steam in Season 8. That started to happen in Season 9. Had Mannix stayed on the air longer, we would have also seen a change in the quality of the scripts.