User blog comment:B214/Volume 21 info & spoilers/@comment-3965848-20160726065224/@comment-9595671-20160919021206

Yeah, that's the big part, we don't know if any non-supernaturals died and how many have perished,. With a case like Raynare killing Issei only one person died and she did it while no one was looking, so it would have been hard to question much.

Plus with what I mentioned with how Shiva's pretty much said they can't cover the supernatural as a whole and just a few details (things that could effect faith most likely), and how Azazel's invention proved memory wiping does have a limitation, it's likely the damage is too great.

Plus when you consider Rizevim's given other dimensions the means to attack them like in the EX timeline, it's probably safer that humanity knows so they can prepare. It would be too hard to keep Humanity in the dark and fight the dimensional invaders at the same time, it was already hard to do that with the Khaos Brigade.