Magic and the Mundane
As far as you are able to ascertain there is no supernatural force that mandates that the vast majority of humanity should be ignorant of that other world which exists just under the skin of theirs, of the vampires in blood-soaked sheets, of wicked fey sounding the hunting horn or the dead gathering in anticipation of the thinning of the veil. Indeed the degree of separation is not always the same. What is hogwash and superstition to most of the urban sophisticates of Chicago is a lot more reasonable to people living in traditional communities all across the world from the Arctic Russia to equatorial South America.
The age of industry has come, the age of instant communication and travel faster than a speeding bullet, but it does not touch all places equally just as it does not touch all people. What might be considered a dreadful breech in one place may be uncommon but understood in another. Consider what kind of magic you are showing and to whom and how they might react in the context of their beliefs. Even within the same general location like say Chicago a devout Christian, a lapsed Muslim and someone who is interested in New Age spirituality will see the same event in different ways
OK, but the vampires eat people equally, why isn't there a consensus on 'giant bat monster bad' at least? Because the giant bat monsters like it that way and so does everything else that thinks of humanity as a snack or an amusement.
Most of the powerful supernatural factions the signatories of the Accords do things that the vast majority of governments and the vast majority of people would find objectionable and so they would rather mankind scoff at tales of vampires and relegate the fey to the realm of Disney Animation. Do note however that a majority of people even in the modern world believe in ghosts. That is because ghosts do not have a voice in those counsels and any clean up after a haunting is far less through than say a vampire killing in a public place.
Looking at it from the other direction what happens when something slips through the net? Say a bunch of burned vampire corpses end up on the table of the local coroner who being really into both the truth and the scientific method calls them for what they are, not human, not animal, nothing known to modern science. Well he almost gets fired from his job as mentally unsound because no one wants to take the chance of being painted with the same brush, of being labeled crazy.
There
are people out there trying to bring the weird to the light, the Susan Rodriquez' of the world, but the pay is shit, the hours are long and you get no respect. The people who take those jobs anyway tend to be true believers, though not necessarily with the thoroughness of Waldo Butters, they have their own theories and many if not most of them are nonsense, camouflage for the supernatural that they do not even have to pay for, an early warning system when something is about to blow up. If you read about an actual breach in the Midwestern Arcane you have quite a bit more time to do damage control before any more reputable paper gets into it
So to really break things open you need something big, you need something persistent. It has to stick with the public so hard that the government feels it has to act openly... keeping in mind that most governments know more than they let on . They might know for instance that they would be starting a war with multiple world-spanning conspiracies and what might as well be the Alien Invasion from Tir Nan Og,
So in conclusion it is really really hard to break the masquerade wide open, though you should be careful how hard to poke the veil so as not to get its enforcers on your case.