Um... Didn't you read the story of Saul, later known as Paul? God revealed himself to him in a great light...and Paul was blinded. He can reveal Himself physically if he wants to, but there's always a reason for it and a purpose. One thing's for sure, you won't see his face, but you will read His word and you will feel His presence, and he will touch your soul, and he will do physical things that will also affect your spirit, without him having to show his physical form (which is Jesus).
Maybe he doesn't do it because there's enough proof in the sky to reveal how real he is.