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?

Cassie is way better than Gregory (A rant) : r/fivenightsatfreddys

FNAF: Security Breach Ruin DLC - What Is The Mimic & Who Is Helpi?

Gregory Gets Destroyed By Cassie FNAF Security Breach Ruin DLC

SECURITYBREACHRUIN

FNAF SB Ruin - All Endings Explained; Scooper Ending and More

Any theories on who Cassie is and why she's helping Gregory? : r

Roxy worried about cassie - Imgflip

cohost! - #ruin

Five Nights at Freddy's: Bad news for Xbox and Switch fans

Gregory, Five Nights At Freddy's Wiki

Ruin Endings Explained - Five Nights at Freddy's: Security Breach

Five Nights at Freddy's Security Breach - RUIN

All 'Five Nights at Freddy's: Security Breach Ruin' Endings, Explained

All FNAF Security Breach Ruin DLC endings, explained - Dot Esports

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