They don’t , if they found the bible as dubious as atheists then they’d be unlikely to remain theists. What’s interesting is they are happy to disbelieve identical claims form other religions involving other deities. I have even see people with wildly differing beliefs team up again atheists here, as if they are fighting the good cause, the irony is palpable, as theists are the ones claiming other theists are wrong, not atheists who generally just don’t believe the claims they make, and the arguments they present.