Much like we do not know the majority of what is in our waters, that doesn't mean that whats there is non-existent. God could very much be real as the possibilities of this world are endless. For example our planet is the only one with living beings (that we know of).

God is a supposedly superior being, why must he? it is up to him to do as he pleases, he has a much free will as we do. If he chooses not to talk to the ones he has created and feels that they should be allowed to make their own choices and choose what to believe then by all means he can do just that.