It would literally destroy them; it would shock them; it would render them insane. For everything they have ever known, and thought they understood, is now meaningless. It would be extremely cruel to do this. So it's perhaps better to let them believe that the lies are the truth; and let them carry on existing with those distortions of truth.
That sadly is where most of mankind sit with regard to the true nature of planet earth and its environs. You can't suddenly burst that bubble by telling them all that everything they have ever known about life is actually a lie. It would spread mass panic and revolt. The suicide and murder rates would rocket overnight. So sadly, this is the reason why the pretense about this reality is kept up publically, and the true nature of life is being fed drip feed to those who can accept the truth.
And this drip feed of real information is likely to continue for many generations to come; so the perceptions and ways of thinking are changed gradually ... it is possibly the only way to enable mankind to wake up out of its slumbers.