Why Did Gregory Kill Cassie in FNAF: Security Breach — Ruin?

In one of the endings for 'FNAF: Security Breach — Ruin,' players watch as Gregory betrays and supposedly kills Cassie during her escape. But why did he do it?

FNAF DlC Ruin, Wiki

Ruin - News - IMDb

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The Security Breach Ruin DLC ending we needed by AwesomeGameDude10

What Happens When Gregory Betrays Cassie Five Nights At Freddy's

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bird enthusiast — Not gonna lie, the main ending of fnaf Ruin

DLC Cassie is now confrimed as Gregory's friend :D by NoriNori77