In general, many Epic Bosses control abilities like Xiao Ruyi, and the seal that's now broken could actually allow ghost creatures to escape.
But not a single one has come out, which clearly indicates that the entity inside already knows what the environment outside is like.
If only a few were to run out, they'd likely be greeted by the Flame Lords with a massive explosion and sent packing.
Having been sealed for thousands of years, none of them would want to be killed just as they managed to escape, so they're all waiting for an opportunity.
Without any powerful ghosts making the first move, the weaker ones, they wouldn't become the scapegoat even if they were to die.
They are creatures that have existed for thousands of years, each one cunning and extremely afraid of death.
If they weren't afraid of dying, having been sealed for so long, they would have committed suicide long ago.
Waiting, the whole battlefield fell into a strange and eerie atmosphere.
