If the evidence for God was "irrefutable" it would interfere with human free will to decide whether to believe or not believe. Exactly what that irrefutable evidence might look like, I don't know, and I would love for someone to tell me. For many people the universe is itself evidence enough to believe in an almighty creator, the qualities of whom are reflected in the creation. And for those who are unconvinced or don't wish to believe in such a creator then "plausible deniability" allows them to do so. Ultimately, the situation is a win-win for everybody!