NCIS & Female Characters

As news travels down the pike that the NCIS:LA spinoff has dropped Louise Lombard as the team leader/main cast member, I find myself pondering the women of NCIS. The women of NCIS are all strong, capable, usually tough and physically strong - and they all wind up dead. Or missing.

Kate Todd - Secret Service - Presidential Detail, then NCIS.  Shot.
Paula Cassidy - NCIS - blown up in a self-sacrificial act.
Jenny - top level agent, first female director of NCIS - killed in a gunfight.
Col Hollis Mann - high ranked Army officer - character written out without explanation.
Ziva David - kick ass Mossad agent - dismissed from NCIS and last seen as a terrorist's hostage.
Macy - top NCIS agent and team leader - written out. No explanation yet.

It's rather disturbing that such good characters are created, but except for Abby, they all get kicked to the curb. What gives, NCIS?