Cersei is the last big bad. By that I mean, even though the Night King is set up as the ultimate bad guy in the series, no one is invested in his death. Cersei on the other hand has seven seasons worth of character development backing her. Everybody is waiting for what is essentially the last big satisfying bad guy death. I don't think they're going to let us have it till the end of the eighth....giving her time to maybe do some more shit that reminds us how much we hate her, like maybe having Bronn killed or some other B level character we love....