Why do people talk shit about their abusive partners, yet refuse to leave the relationship?

Maybe it's just the people I surround myself with, or maybe 2025 is driving people to the brink of insanity; but why do (predominantly) girls refuse to leave their partners who they SWEAR they hate?

To put it into perspective, I know this nice girl, Reina, who has a sack of shit boyfriend and she knows it. It's not even like she's blinded by any of his good qualities. No. Not at all. She's completely aware that he's a bad person and will use any given moment to express that. If you hate him (for valid reasons or not,) why not just leave? He's an asshole and you despise him for it.

Now it's a completely different story if you're in a relationship where you're legitimately unable to leave. I'm talking about like "I'll fucking kill you if you leave me" type thing. Not online relationships. Y'all got nothing to worry about. 

I feel like teen girls in general have a habit of maintaining this whole "#Ihatemybf" bit to the point where they convince themselves that they actually mean it. 

P.S. Don't bring up Stockholm Syndrome. It's not Stockholm Syndrome if you hate your abusers guts.