I am an atheist. If there really is a "god", why is there no physical proof that he, she, it ever existed? Except for written words ... which, for all that we know, could be all lies so people can feel better about themselves.
Are you supposing that, if something exists, it has to be possible to prove that it does? I would suppose not. So let us rephrase the question: Why isn't there compelling physical evidence that God exists? Some people think there is: The universe itself constitutes such evidence. And if that doesn't seem compelling, what would? The deeper question, however, is why one would suppose there had to be compelling physical evidence of God's existence. There is no compelling physical evidence, so far as I know, that there are such things as nondenumerable ordinal numbers. I suppose nonetheless that there are, and it seems odd to ask for physical evidence that there are such things.