I think it's just she isn't that likeable or sincere (and has always had that problem since xfactor) plus she hasn't improved, if anything she has got slightly worse. The people who start out very good rarely win, people like to get involved with someone's 'journey' and also someone who has advanced and improved is arguably more deserving than someone who hasnt
I have to say I find these judgments about whether she is sincere or not to be galling. She is an emotional and dramatic person (and she can be OTT at times) for sure, but for me at least, it's genuine emotion and unless we've had close dealings with her, I'm inclined to give her the benefit of the doubt.
It's nice to see Jon Robyns, Sandy Grigelis, Sarah Goggin, Tristan Gemmill and Rachel John have been on Twitter to defend her and stress how genuine she is. If she was a not nice person, I sincerely doubt they would bother.