She's not naturally sexy, and I also think it's because she's not as "thin" (I don't know how to explain it) as Selena or Ariana. I still see people every day calling her fat. I'm not shading her or anything, but society doesn't want people who they consider "not thin enough" to show their sexy side, which is stupid and so degrading
Also, people hate her for actually speaking up about certain issues, but sometimes she can be a little dumb.