The world has never known what it’s like to have a powerful being in front of them, one that is not human and possesses powers strong enough to destroy every human on this planet in seconds. The reason why we have kept them stored in underground facilities is that they are actually good and they willingly decided to allow us to capture them. They know that their powers would be used for the wrong kind of reasons if they ever came out into the world again.
We believe that the power that these beings can unleash is far too great and wonderful to even allow humans to see it at all. We need to see an evolution of the species, that seems to be going to take a few million years for humans, while other species did it in a just a few hundred thousand years.