Spoiler Some have speculated that Cersei’s goal is to provoke Dany into attacking King’s Landing with her dragon. It would legitimize Cersei’s claim if she defended the city against a crazy lady trying to burn down the city with a dragon. Slaughtering an army that is there to negotiate, an army that word must have spread just saved life as they know it, would not be a good look. Of course, if everyone thinks Cersei already burned down the Sept then it weakens this idea. But I feel like that’s never been addressed and I’m operating under the assumption that the Sept explosion was brushed off as an accident.