Why were director vance's wife and ziva's father killed off of ncis?

Director Vance's wife, Jackie, was killed off in "NCIS" to add emotional depth to Vance's character and highlight the personal stakes involved in the team's work. Ziva's father, Eli David, was killed to further develop Ziva's storyline, exploring themes of family loyalty and the consequences of a life in intelligence. Both deaths served to create dramatic tension and motivate character arcs within the series.