User blog comment:B214/Volume 22 spoilers/@comment-9595671-20160829080406

Oh boy, I just learned two (or one depending on the accuracy of the first) major things.

The first... not sure how accurate it is, we may honestly need Volume 22 fully translated first since this could be misread, but despite everyone's efforts, the supernatural world may have actually been exposed to a level they couldn't cover it up due to the media catching it.

I get they can erase memories, but to do that for the entire world would be... well, Trihexa implies Great Red can't do everything. Plus I think they need to know who to erase the memories of, otherwise it might have bad side effects. Hence why Raynare killed Issei when no one was around.

The second? The UL's invasion in EX is the result of Rizevim and the Evil Dragons' last middle finger to everyone by sending them teleportation techniques to their world after making contact. He basically had a back up plan in the case Trihexa was actually stopped.