It's obvious that
Cersei
could have killed
Daenerys
with the
scorpions mounted on the towers of Kings Landing and thus ended the war.
Are there any legitimate in-universe reasons why she didn't? Seems like the writers just don't care anymore to me.
EDIT: I've been convinced why the war might not have ended, but not why it wasn't done anyway. Assuming
Cersei had the capability to kill Daenerys, Grey Worm, Tyrion and the Unsullied
which the screenplay made it seem like she very much did, I find it hard to believe she would pass up the opportunity to kill the group of leaders we saw.