Personally I'm hoping there's a bit of an explanation for that tonight because I think it's the one misstep in a spectacular season of TV so far.
From what I've heard and read this week it sounds like they just wanted a big spectacle to fit with the episode 9 trend from GOT and didn't really think it through properly.
that's exactly what they did and it made no sense whatsoever - tho visually an awesome scene and if it was story appropriate to pyro the lot of them would've been red wedding epic, but as it wasn't, absolutely pointless and stupid and beneath the quality of the show in general
im hoping it's a mistake they learn from going forward in subsequent seasons, they've got a lot more right than what they've got wrong and what they can garner from that mistake is that story trumps spectacle. Story appropriate spectacle can be spine-chillingly wonderful but it is the story that has to do the heavy lifting, let the spectacle deliver the coup de grâce, GOT at it's very best demonstrated that perfectly, all the fan wants really is that it all makes sense within its world, and then we'll buy in to anything. That's the art of suspending disbelief.
And then there is this - showrunner Ryan Condal said, “She knows if she sets fire to that dais, she ends any possibility of war and probably sets peace throughout the Realm, but I think probably doesn’t want to be responsible for doing that to another mother"
Yeah... milk of the poppy talk kicking in there
on a more technical sidenote - i hope someone has a word with the fucking director that likes to shoot his nightscenes in daylight then colour grading to make them look like night, as i cant see fuckall and apparently no one else can unless they own an OLED tv, he did it in GOT (you know that battle where you cant see fuckall) and he done it with the dragon/beach scene in HOD. After all the hard work is done you'd think they'd want us to see it.