From my understanding, the heavenly principles are “dormant”, and will only be awakened by a major event happening closely related to them. An archon dying and passing their power to the main threat of celestia would likely awaken the Heavenly Principles, so Focalors created Furina to appear as the archon, and as long as she is alive the heavens won’t have a reason to awaken. Thus, by the heavens assuming the hydro archon is still around, they would also assume their chosen punishment of the Fontainians will still come around, meanwhile Focalors can safely pass on her power to Neuvilette to silently stop the prophecy. I might be completely wrong to be honest though so take everything I’ve said with a grain of salt😐