Why Lost Really Killed Off Ana Lucia & Libby (It Wasn't Their DUI Arrests)

screenrant.com:

Contrary to popular belief, Lost season 2 killing off Ana Lucia and Libby so suddenly was not due to the DUI arrests of actors Michelle Rodriguez and Cynthia Watros. Ana Lucia Cortez and Elizabeth «Libby» Smith were introduced into the story proper early in Lost season 2, as two survivors from the tail section of Malaysia Airlines Flight 370. Their survival had been unknown to Jack, Kate, Sawyer, and the rest of the main group, who crashed on a different part of the island.

Ana Lucia quickly asserted herself as the leader of the tail section survivors, but also quickly drew ire from audiences for her overly combative and antagonistic behavior toward the main characters. Her accidental murder of Shannon, who had herself been partially redeemed due to her love affair with fan-favorite Sayid, furthered the backlash against Ana Lucia. By contrast, Libby developed a rather charming relationship with Hurley, which saw the two growing closer romantically prior to Libby's sudden demise by gunshot.

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Said gunshot deaths for Ana Lucia and Libby came in the Lost season 2 episode «Two for the Road,» as they were shot by the normally friendly Michael, who had been coerced by The Others. This episode aired mere weeks after Rodriguez and Watros were both arrested for driving under the influence of alcohol, so the common wisdom quickly became that they had been kicked off the show due to those charges. In actuality, Ana Lucia's death had been planned from the beginning, as Rodriguez didn't want to do more than one season. The decision to kill the mysterious Libby as well was due to Ana Lucia's unpopularity, as producers thought Libby's death would be a more shocking