@Ultrabenosaurus It actually
is explained why Kail doesn't go public with the Melra worshipers' plots and repeatedly at that, albeit indirectly; though I'll admit it took me to my current re-read to notice it. Put simply, Kail is positively desperate for humanity to be able to put up a strong, united front against the demons, instead of being steamrolled like they were in his previous timeline. And, looking at the flashbacks we get of the war and how grim things were, it's understandable. Remember, he murdered King Remanos simply because the king's actions during the war caused insane loss of life amongst the races fighting the demons, so there's very little he won't do in order to achieve that goal (while also ensuring those closest to him are safe). Publicly claiming that the Melra worshipers were behind the dragon attack is the kind of thing that has the potential to bring all his efforts to naught.
Consider this: how do you identify a Melra worshiper? Their medallions. Okay, so what happens when they simply stop carrying them? You end up with the
incredibly ugly scenario of systemic religious persecution the likes of which some of history's most brutal wars have been fought over. Before this, they've just been minor nuisances, but if it becomes public that they were behind a dragon attack that likely killed hundreds (if not more), the populace will
demand that they be rooted out like rats in a storehouse; many would also take it into their own hands, hunting down and lynching any "Melra worshipers" they came across and many others would seize the opportunity to rid themselves of anyone they didn't like. And that's the kind of thing that, once it gets started, doesn't die down quickly, so it's the last thing Kail would want.