Theists don't accept this because they think that there is a mystical world that doesn't have to answer to science or facts.1. If god exists, there is evidence of his existence.
Why do I make this claim? Well, god is supposed to be all-knowing, all-powerful, and involved in our lives, answering our prayers.
I would not make a similar claim about life on Mars. It could be quite possible life could exist on Mars and escape our discovery.
2. There is no evidence god exists.
3. God does not exist.
It is after all a form of denial. I mean it's tough for a hardcore theist to admit to themselves they've been wasting their lives chasing after some old human's fantasy.