Because it doesn't make much sense? Why would she burn all the good rapport she build up with him just for a singular fuck sesh, when her goal is the protag's love? Like, I can understand if she was going nuclear and go "If I can't have you no one can" but she clearly is still obsessed with mr white bread over here and is still trying to get him to like her. Iunno, shit don't add up.Love makes you do some stupid shit.
This was her game the whole time anyway. Did no one seriously catch that? She was totally pushing towards them being together, solely so she could pretend to be his gf and get him to fuck her. That's the only way it was gonna happen.
But oh "best girl" yall fucked lmao (I ain't judgin but I am)